Steve Backshall: I'm Steve Backshall, a naturalist and explorer.

Wow.

What a place.

I've come to Saudi Arabia, an ancient desert kingdom.

Steve: That is absolutely incredible.

Steve, voice-over: For much of the last 90 years, it's been off limits to naturalists and explorers.

But now the country... Ooh!

is opening up.

Steve: Just one wrong footfall or handfall, and the whole lot will go.

I'm here to seek evidence of the ancient humans who traveled across this rocky land... Steve: This is huge.

on the first migrations out of Africa... Oh, this is utterly, utterly amazing.

when the Arabian Peninsula was a very different place.

Steve: No!

Woman: What is that?

So perfect.

♪ ♪ Steve: There is something very, very special about the desert at sunrise.

There's a quality to the light, a bitter, biting chill in the air.

And where we are right now is particularly special because up until 2019, it was completely closed to the outside world.

♪ Steve, voice-over: Saudi Arabia's landscape is so much more than desert.

It's home to sprawling volcanic lava fields and imposing sandstone pinnacles.

Now new research is revealing an unexpected history.

These scorching deserts were once green savannas, teeming with all kinds of life, from wild cats to gazelles, ibex... ♪ and even people.

♪ This desert was a pathway for the first human migrations out of Africa.

♪ Studies suggest our ancestors may have left Africa over 120,000 years ago, passing through here before spreading out to populate the rest of the globe.

♪ I want to explore this area and find evidence of these people and animals to understand more about these arid plains and their important place in history.

Steve: Look at that!

It's just mesmerizing.

I mean, even the rocky outcrops, all sculpted by the wind and sand, are dazzling of themselves.

But as you start to look closer, you notice carved doorways, openings, inscriptions.

All of this landscape has been altered by human hands.

But a very, very long time ago.

Steve, voice-over: My journey begins in the ruined city of Hegra.

It's been a key waypoint on the route of peoples through the Arabian Peninsula for thousands of years.

Once an important trading post, all that remains is a scattering of giant tombs.

Right now while I'm here freezing, Aldo is essentially standing in his underwear.

Mate, you forgot your coat.

What happened?

It's in the bottom of my bag, and it was all about the quick stop.

[Laughs] Steve, voice-over: Joining me is rope safety expert Aldo Kane-- Wow!

And Saudi Arabian geologist Hala Alwagdani.

Do you see right on top of the door?

There's 3 symbols, and they've been carved there to scare people off from going into the grave.

Steve, voice-over: Local expertise like Hala's is crucial to the success of this expedition.

See that there's a plaque right on top of that bird that's on top of the door?

Yeah.

That also has inscriptions that says if you go in, you will be cursed forever and ever.

Here we are years later going in.

[Laughs] Steve, voice-over: Still not fully documented, Hegra is an archeologist's dream.

Steve: It is absolutely incredible.

Hala: Yeah.

And nowhere is more spectacular than the towering al-Farid tomb.

♪ Built by the Nabataean people around 2,000 years ago, this is the largest tomb of its kind in Saudi Arabia.

Hala: So this wasn't a complete grave.

It was complete on the outside, but you don't find a place where the grave would be in.

But it's not--it's not as grand as it is on the outside.

It seems like the façade is always great, but when you go into the inside, it's just a snug room for them to sleep forever.

Steve: It's still pretty special that this cave has been made out of the rock with a hammer and chisel.

Yeah.

2,000 years ago.

Exactly.

♪ Steve: Where we're standing right now is a globally significant, important place for ancient history.

And anywhere else, if this was Petra or the Pyramids or Angkor Wat, you'd expect to be here with a significant amount of other people.

And it's just us.

There is nobody else here, which is unparalleled.

There is nowhere else in the world of this degree of historical significance that is so unknown.

And to have it completely to ourselves is something you can't overestimate.

♪ I mean, it gives me chills, just the thought of what we might see and what we might find.

♪ Steve, voice-over: This tomb was raided and stripped of artifacts long ago.

But that makes me all the more eager to explore parts of Hegra that are harder to get to.

Man: Here we go.

[Drone beeping] As spectacular as these landscapes are from the ground, they take on a whole different perspective with a bird's eye view.

So Abdul is sending the drone up now to look down on top of these peaks from above.

What's that there?

Is that a wall?

Hala: Looks like a grave.

No, look at that, look, it's in a big curl, like a kind of snail shell.

Oh, yeah.

What is that?

I don't know.

Can you zoom in?

And there's more of them.

Abdul: 1, 2, 3.

Ahh, a bunch of them.

Can you get a little bit closer to that?

They're the most remarkable geometric structures right on the top of these peaks.

So that's two.

It's almost ubiquitous that high places tend to be more sacred because they're closer to the heavens and closer to the gods.

And seeing the pinnacles of all these peaks covered with so many artifacts is really enticing.

The thought of what must be up there and how few people will ever have seen them for real on the ground.

So I guess we just need to find if there's a relatively easy way up.

Let's go around and find out.

Yeah.

♪ Steve: So we put a call in to the local archeologists who specialize in the Nabataean history of the area.

And they don't know anything about what's up there.

It's news to them that there's anything there at all, so this is quite intriguing.

♪ The rock looks nice, but it's so crumbly.

Yeah, this could be trickier than it looks.

♪ Aldo: The thing is, the climbing, if it was on good rock, looks easy enough.

But by the very nature of how this rock is made, it's--it's completely fragile, and you can see under his feet, it just completely slides off.

And all of the, uh, areas for protection are pretty brittle.

♪ Steve, voice-over: But if we want to make it to the top... Steve: OK, take it!

this is the only way.

Steve: Keep going.

Keep going.

Aldo: Yeah.

More.

Yeah.

Hala: OK. OK, climbing.

Yeah.

♪ Steve, voice-over: One by one, the entire team make it past the first hurdle.

♪ Wow.

Come and have a look at this, Hala.

It's beautiful.

What a landscape.

♪ Wow.

The one we're heading to is above us.

So, I think we head up there.

And how we do the last little bit to the very top, I don't know.

♪ Oh, it's just there.

Just there.

Yes.

It's like on all sides, it's just huge rock, though.

Would you be... Would you be happy crossing over on this?

Yes.

Yes, I would.

I mean, the consequence of a fall is...bad.

♪ Um, I might need a hoof to get up this.

♪ Thanks, mate.

You're welcome.

♪ Do you know what?

I think that this--this little wall here is like an ancient staircase.

Aldo: That makes sense.

♪ Just whether I trust it or not.

The big problem is just if this--if this pile goes.

♪ I mean, that's been there for hundreds of years, right?

Aldo: In theory.

So it's not gonna go, is it?

Everything goes at some point.

Ooh!

Ohh.

♪ [Exhales] Steve, voice-over: I'm so close to the top.

I'm not gonna give up now.

[Exhales] ♪ Yes!

Aldo: Are you up?

Yes, I am.

♪ Well done, mate.

Oh, this is utterly, utterly amazing.

♪ Whoa.

It's like climbing on sugar cubes.

♪ [Grunts] Steve: What do you think of that?

Amazing.

♪ Just be careful teetering around that corner.

Yeah.

♪ Steve: So it's instantly fairly obvious that this is very different to everything else we've seen here.

All of the Nabataean ruins that we've seen have been focused around-- around the afterlife, you know, they've been-- they've been graves, they've been burial sites.

That's not what this is.

Um, you know, you'd have to be fleet-footed to get up here, but you wouldn't come up here with a body.

You know, this is somewhere that's high because it has a great view, a vantage point.

And these walls are protection.

From a military perspective, I would say this is a hundred percent a lookout tower, uh, or a lookout post.

It's like pretty strategic across all of the highest points almost with a full 360-degree arc of view all the way around.

And these rocks will provide cover from fire, in theory.

The question is, when does it date from?

How old is it?

Oh, check this out, mate.

♪ You see those?

♪ Man: Hmm.

What is it?

They're buttons.

They're old, metal buttons.

♪ So, obviously, you know, there have been people up here within, I would guess, the last hundred years.

It's possible that this could be Ottoman.

But whether it was built originally several thousand years ago, and then rebuilt, I don't know.

But the local archeologists know nothing about this site, nothing at all, so anything that we can bring down as evidence--photos, videos-- will give them an idea of what this is.

Steve, voice-over: These buttons could date from just a hundred years ago in the Ottoman era.

♪ The watch towers themselves were probably used as far back as 2,000 years ago.

But even that is just recent history compared to where we're heading next.

♪ We're traveling south to look for evidence of the ancient humans who passed through here... Wow.

What a place.

and find out more about Saudi Arabia's ancient climate and its once rich ecosystem.

♪ This hasn't always been a scorched desert.

Thousands of years ago, a lattice work of rivers crossed the terrain, allowing animals and people to survive.

That era is long gone, and Saudi Arabia's interior is now a vast sandy desert cut through with stark volcanic lava fields.

But below ground, unprotected from the ravages of the harsh climate above, there are caves that could still hold evidence of those people and wildlife.

Aldo and I are taking to the air to scout potential ways into this subterranean world.

Radio check.

Radio check.

Aldo, on radio: Radio check, yep.

Can you hear me?

All right, we're good to go?

Yeah.

[Helicopter whirs] ♪ Steve: As you're flying over the desert, you see these shapes, these geometric shapes, which are obviously too neat, too perfect to be natural.

And it's believed that these were put in place by Stone Age, possibly Bronze Age, peoples thousands of years ago.

Steve, voice-over: While their meaning remains a mystery, they're clearly a marker from the migrations that passed through Saudi Arabia.

So down below us... that line of vehicles there is the rest of our team.

Steve, voice-over: Lead by Hala, the ground team is transporting the 3 tons of specialist kit we'll need.

We're driving up to that volcano.

And the roads aren't exactly roads.

[Laughs] Steve, voice-over: We're all heading to a meeting point in the Harrat Khybar lava field, where geologists believe the longest lava tubes in Arabia could be found.

♪ Wow.

There's a biggy.

Look at that there, that big one.

So these are some of the volcanic craters, obviously extinct now, but super dramatic.

And this is where a lot of these lava flows would have originated.

There's another one over there.

♪ Amazing.

♪ Steve, voice-over: During a volcanic eruption, the outside of a lava flow cools down and forms a crust.

♪ As the lava inside continues flowing, it leaves behind a void known as a lava tube.

♪ The lava tubes here can be 40 meters in diameter and hundreds of meters in length.

♪ We want to discover whether this underground labyrinth still holds signs of life from our ancient past.

What we're looking for is a skylight, a hole that drops down into the lava tube beneath.

And our aim is to get inside.

♪ Aldo: Here we go, look.

You see that sort of hole?

♪ Wow.

Wow.

Yes, I see it.

Yeah.

There's definitely a line of them, isn't there?

♪ Steve, voice-over: This is what we've been looking for-- Yeah, we're nearly there.

Yeah, and it runs up that direction, doesn't it?

Steve, voice-over: several openings that line up... We'll mark that on the GPS.

a sign there's a lava tube running beneath.

Yeah, this must be the start of it, don't you think?

Oh, wow, yeah.

But to be sure, we need to get boots on the ground.

Man: Finally you made it, huh?

Finally.

Hello!

Joining us is geologist Mahmoud Alshanti, a world-leading authority on this volcanic underworld.

Very good.

Nice to meet you.

Mahmoud and Hala believe this area might be home to the longest lava tubes in the Arabian Peninsula.

♪ They want to map everything they find.

♪ And I want to see if these caves hold evidence of past life.

Here we go.

We share what we've seen from the air...

Some of them, they have easy access, OK, entrances.

and agree on our first lava tube.

So you think that this area here gives us the best chance at exploring new-- Yes, yes.

unmapped lava tubes?

Yes, yes.

Yes.

OK. ♪ Steve, voice-over: With 4x4s loaded, we set off.

♪ We're heading 15 kilometers north to a giant skylight.

♪ We hope it's a way in to an unmapped lava tube.

♪ Ahead of us is a razor-sharp landscape of basalt rock created by the last volcanic eruption 1,400 years ago.

[Engine revving] Yeah, come this way.

Maybe this way a bit.

Good work.

Good work.

Steve: This stuff is so sharp.

And if you did run the side of the vehicle along this, it would just peel it back like a can opener.

Excellent, guys.

[Men speaking Arabic] [Horn honks] ♪ Steve: Well, we're certainly not going any further in that direction.

That is a very big hole.

Could be exactly what we're looking for.

♪ Steve, voice-over: From the air, this entrance looked easily accessible, but up close, it's looking fragile and dangerous.

Steve: Well, that's a big hole.

Aldo: Yeah, it is.

Steve, voice-over: We're facing a 20-meter vertical drop into a void with collapsing sides.

Very nervous at the edge here.

All of these fractures are weak points that could just go, couldn't they?

Steve, voice-over: To get the whole team down safely... Yeah.

we'll need find the strongest part of the rim.

Mahmoud: Steve?

Yeah.

Maybe this one is more stable.

Mahmoud and Hala's expert knowledge of the rock here is vital.

Exactly here.

You see this?

Maybe that one is more stable and safe, I think.

That one.

Oh, yeah.

Steve: Yeah.

That's--that's quite good from here.

♪ You go in sideways, yeah?

Straighten up.

Steve, voice-over: Aldo has teamed up with rope safety expert Justin Holt.

With decades of caving and rigging experience between them, we're in safe hands.

What do you reckon for rigging, just come straight off the wheels?

These ones.

Do you reckon if we have, like, a bit of floating anchor?

Yep.

Steve, voice-over: The rim's too flaky to rig from.

The 4x4s make a perfect anchor point.

♪ Aldo: How much?

Justin: Keep going.

Steve: We are working in an area where nobody's really been.

And the edge here, you know, is a collapsed roof.

If it hasn't gone in the past, it will go at some time in the future, which means that it's unstable.

And not knowing which parts of it are, you know, quite strong and you could drive a truck on and which ones would go with a touch of a finger is almost impossible.

Steve, voice-over: For Hala and Mahmoud, this is an opportunity to study the geology of an unexplored lava tube.

There you go.

Perfect.

Saudi Arabia's longest recorded tube is 3.3 kilometers.

They're hoping this one is longer.

Let's do it.

Let's do it.

Steve, voice-over: For me, it's a chance to see if anyone or anything has ever been in this cave system.

♪ Just, happy?

Justin: Happy.

♪ OK.

Does that feel nice and-- Yeah, it feels good.

It feels good.

♪ Steve-o?

Yes, mate?

Just let me know if it-- if it doesn't clear on the way down.

Yeah, cool.

How's it look?

I mean, if any of these blocks go, they are vast.

Yep.

♪ Aldo: OK?

Yeah.

Rope free.

♪ Slowly.

That's it.

Steve: How you doing, Hala?

Smooth.

Steve, voice-over: One by one...

It's peaceful down there, huh?

It is.

Wow.

Steve, voice-over: we descend into the mouth of the lava tube.

We made it down.

Steve: We did.

♪ Mahmoud: Whoa, this is a big one.

Steve: This is huge.

Yeah.

It's so much bigger than I expected a lava tube to be.

♪ Just gigantic.

♪ 13 meters.

Mahmoud: To here?

Steve, voice-over: While Hala and Mahmoud begin mapping... 13 meters and a half.

I'm on the lookout for signs of life.

Whoa, what's that?

Mahmoud: Another opening.

Another collapse.

Yeah.

♪ Mahmoud: How is it up there, Steve?

Steve: So there is a big dark hole ahead of us.

It looks like it might kink left.

Um, or it could be a giant collapse.

Aldo: Yeah.

Look up ahead.

Do you see that fault cutting through the middle of that entrance?

Well, this collapse is right above my head.

Mahmoud: This is a risky one.

That's just a collapse waiting to happen.

That's very dangerous.

Aldo: Just because the lava tubes are old doesn't mean that these collapses happened millions of years ago, right?

They can happen all the time.

Mahmoud: Recent, yeah.

Yeah, it happens.

Hala: It's definitely unstable, and we don't want to be here if it's dangerous.

Yep.

Steve, voice-over: It's taken a huge effort to get down here, but Hala and Mahmoud are convinced the ceiling is a serious accident waiting to happen.

♪ We have no choice but to turn back.

♪ Aldo: Just be careful with where you put your feet.

OK. Steve, voice-over: By the time we get back to the top, it's already getting dark.

Justin?

Yes?

OK, Hala is on.

OK. And she's ready to be hauled now.

OK. Steve, voice-over: Fortunately, the rest of our team above ground are happy to lend a helping hand.

♪ [Speaks Arabic] ♪ Justin: All right, you're up.

Next.

OK, you're good.

Cheers, Just.

Everything was creaking, crumbling.

It was really hard to get any sort of confidence in that surround.

It just...everything just looks like it's about to collapse at any second.

It was a little bit nerve-racking, to be honest.

Man: It was like-- it was so loose down there.

You never know when it might fall.

So, yeah, very happy to be out.

Not a comfortable place to be.

[Indistinct chatter] Steve: This set up is amazing.

We have to own it to Mahmoud.

Aldo: These rugs.

I'm loving the rugs.

It's such a great idea.

It would never work in West Wales.

No.

Damp.

[Laughs] ♪ This is so great.

Completely out under the stars, desert night.

Doesn't get any better than this.

♪ Justin: Ahh, I haven't put that in.

Steve, voice-over: It's first light, and we're striking camp, keen to head out to find and explore our next lave tube.

Where do we go?

[Speaks Arabic] Steve, voice-over: From our aerial recky, we spotted a potential entry point 7 kilometers to the north.

But we've got to get there first.

♪ [Speaks Arabic] Steve: Ahh.

Man: No, no, no, no.

That is the most fingernails- down-a-blackboard sound I think I've ever heard.

Car undercarriage scraping over razor-sharp lava.

[Speaking Arabic] Ahh, look at the front as well.

That's...sketchy.

Easy, easy, huh?

[Speaks Arabic] To make matters worse, what he's driving over is a crust of lava like this thick, and get it wrong and the whole thing would just collapse.

And then we would be in big trouble.

We are hell and gone from anywhere.

[Engine revving] [Man shouting in Arabic] What do you think, Steve-o?

You got this, Aldo.

That looked pretty tough.

If you come through that reasonably quick, you'll be all right.

And then this bit here super slow.

All right.

Should just tell him, "No, just go.

Just go hard.

All the way through.

Third gear."

Yes, go, go, go, go.

That's it.

Nice.

You're good.

You're good.

What do you think, Hala?

[Laughs] Fun stuff.

What do you think?

You've seen 6 cars to this.

I think I'm very, very glad I'm not driving is what I think.

Steve, voice-over: It's taken us all day, but we've reached the second lava tube, and it's one we can climb straight down into.

So I guess for now, we'll set up camp just nearby, and then first thing in the morning, get down and check it out.

♪ This is a good sandy spot.

Oh, it's getting cold already.

Steve, voice-over: It's winter, and at night, the temperature plummets to well below zero.

So, yeah, the secret is get the tent up as quick as possible.

Basically, there's a bit of sand on top.

It's like an inch.

And then it's back down to solid lava again.

So just gonna have to use my weight to hold everything down.

Camping out slap-bang in the middle of black, jagged lava.

♪ Steve, voice-over: We're up early to put the drone in the air.

We want to scout the most likely course of this new lava tube.

So can you fly in this direction?

A bird's-eye view is what we need.

So that's us there.

Only from up there do we get the true lay of the land.

♪ So you can see the direction it's orientated, can't you?

The sight of further collapses suggests this could be a really long tube.

Can you give us the exact direction on that from here?

Northeast?

Man: The north, the east.

Yeah, so it's northeast.

So you're happy what you're doing then?

You're gonna go across-- Yeah.

the top in that-- is it roughly east?

Basically heading due east.

Steve, voice-over: Justin will lead the topside safety team.

Hiking above ground, he'll track our progress between the two collapses.

♪ What I'll do is I'll try and radio every time we get to a collapse.

Steve, voice-over: It's Justin's job to launch a rescue if we fail to reappear.

So if I'm not out by 3:00, then come and find us.

OK. Will do.

♪ Steve, voice-over: This cave is accessible without ropes.

That's a double win.

It's quicker, and it means ancient humans and animals are more likely to have done so, too.

♪ Saudi Arabia's desert climate hasn't always been so inhospitable.

Thousands of years ago when it was wetter, herds of animals following water would have once roamed this area, and following them, hunters/gathers.

♪ The entrance to this lava tube couldn't be more different to the last.

Mahmoud: Watch your head there, guys.

Just a few meters in and we're crawling.

♪ But not for long.

Amazing!

Opening out before us are perfectly circular and smooth walls.

♪ Hala: 13.

Up to where?

To you.

Steve, voice-over: Hala and Mahmoud waste no time... To here?

Yes.

Thank you.

mapping and attempting to date the cave's geology.

This thing, uh, looks very old.

Very, very old.

So this--you don't think this is part of the new lava flows we saw on the surface?

No, no.

This is older.

How old?

Around 23 million years old.

What?

Yes.

All these cracks being filled with materials proves that this is an old one.

All this materials are old.

So in order to have all this powder, it has to have taken a lot of time to weather it.

Millions of years.

Wow.

Well, that in itself is a discovery, isn't it?

Yes.

What an amazing surprise.

Steve, voice-over: Hala and Mahmoud had thought this lava tube was related to recent lava flows, 1,400 years ago.

♪ The revelation it could be millions of years old is exciting.

It's a window into our distant past.

There could be anything down here.

♪ Steve: Look up.

Mahmoud: Wow!

♪ Wow.

Hala: Yeah.

Steve: That is amazing.

Mahmoud: This is lava stalactites.

Oh, this is the best seen-- I have ever seen in lava tubes in Saudi Arabia.

This is the best one.

How long do you think these take to form?

They formed when the cave formed, when the lava flows were flowing, so that was before it started to fire.

Steve, voice-over: These stalactites are actually little pieces of molten ceiling that dripped down and hardened as the lava tube formed.

Hala: And they're sparkly 'cause of how they mineralized.

For Hala and Mahmoud, this is like striking gold.

Steve: That's extraordinary.

Hala: Yeah.

You don't expect to see that from liquid molten rock.

We can't know whether we're the first to see this, or whether our ancestors gazed on the same thing long ago.

Hala: 36 up till that point.

Justin over radio: Justin, Aldo.

Yeah, Justin, this is Aldo.

Go ahead.

Yeah, Aldo, we've found another hole.

We've just come through the lava tube about 300 meters due east.

Whereabouts are you?

Over.

Um, I think we're probably in the same position.

Yeow!

Hello!

Hala: Hello!

Hello!

Aldo on radio: Can you mark that on the GPS?

Over.

Copy that.

Over.

Yow!

Woot woot woot!

Justin: So we've obviously found this, like, basically a sink hole, collapsed cave into the system.

Our plan now is to continue.

We'll keep heading sort of east/southeast, see if we can find another entrance.

We haven't picked anything up with the drone, so it's just a case of finding any kind of depression, any entrance back into the system.

♪ Steve, voice-over: We're already 300 meters in, but we'll press on as far as we can.

Mahmoud: I'm just checking if this is calcite or gypsum.

Hala: If it's salt or not.

Yeah, this is gypsum.

Secondary gypsum that forms later, secondary, from water up there leaking through cracks in ceiling, OK, and it forms a new--they call it secondary gypsum.

And this is how you tell.

Steve, voice-over: Mahmoud's acid test proves water has been in these caves.

It's a great sign that life could have survived down here.

Mahmoud: Oops, watch this.

There was a collapse here, OK.

But it was useful for the people, the ancients, to keep the water inside.

This is dam.

Steve: So you're saying that this was built up by people to keep water inside?

Yeah.

Those rocks collapsed already from the ceiling.

But why they are in one pile like that?

You don't see it down there.

You don't see it in the middle.

OK?

'Cause people collected to keep the water like that.

Steve, voice-over: This dam is our first indication that ancient people used these caves.

It's a significant discovery and spurs us on.

♪ Unbelievable.

♪ So some of this rock is not permeable, and it does help hold water really well.

And you can see that this has been stacked up.

So some of these quite decent-sized rocks have been added to the biggest rocks that fell down naturally to form a dam, a reservoir.

♪ That is amazing.

♪ Steve, voice-over: Lava tubes would have collected and held seasonal rains.

Crossing these parched plains, the ancients clearly knew this and exploited it to stay alive.

Justin: No, I think we've come to a dead end now, so I think we just head back and see if we can radio the others.

♪ I think it's an...

This is an old one.

Somebody--I don't know if this... Steve, voice-over: The deeper we head into the lava tube, the more we find it was once home, or at least a shelter, for humans.

♪ You think that's a tool?

Yeah, yeah, I think so.

I think it's a tool.

Well, it doesn't match any of the other rock around where we are here.

Look.

That's handmade.

Looks handmade.

This has been chipped here as well, hasn't it?

Yeah, you see.

Yes.

♪ Steve, voice-over: It's a rare find.

Stone tools would have been used during the human migrations in the Stone Age.

♪ So this is some very, very ancient evidence of a fire.

And it's not weathered.

There's still plenty of it sticking out from the side that would lead me to think that it wasn't washed in here, but was part of a campfire inside this tube.

And there have been plenty of pieces of evidence that suggest that Stone Age man used tubes like this as a sanctuary and as a place to find water.

♪ That is intriguing, to say the least.

Steve, voice-over: The reservoir, the stone tool, and the campfire are clues that build a picture of how people lived underground here long ago, evidence of our ancestors from a forgotten era.

Mahmoud: Watch out.

Watch out.

What happened?

Steve: It just fell under my foot.

♪ Steve, voice-over: Encouraged by our discoveries, we push on.

♪ Whoa, that is a big pile of nasty.

♪ Oh, what's that over there?

Oh, oh, my goodness.

Oh, that's cool.

That's very cool.

It's a cat.

You mean this is a wild cat.

This is a wild cat.

Oh.

Yeah.

[Speaks Arabic] That's amazing.

That's a really, really amazing find.

We should get--we need to get some photos of this.

♪ I guess we're getting an intriguing portrait into changing time in this part of the world.

So Saudi Arabia hasn't always looked as it does right now.

Steve, voice-over: This landscape was once a green savanna with rivers and lakes.

It supported herds of animals and allowed early humans to migrate across the globe.

But these caves remain the same.

They are an extraordinary repository, a museum, of the natural history of this part of the world.

Steve, voice-over: The stable conditions in these tunnels are perfect... Whoa!

Check that out.

preserving evidence of the ancient history here.

So this is a remarkable animal.

I can tell by the two front teeth here, it's a hyrax.

Hala: OK. Aldo: Hyrax.

Yeah, yeah.

But it's mummified, so, you know, definitely hundreds, possibly thousands of years.

Steve, voice-over: We keep moving.

How many kilometers in are we now?

Aldo: Just went out to 3 kilometers.

Steve, voice-over: The longest lava tube to have been mapped on the Arabian Peninsula is 3.3 kilometers.

We're now short of this by just a few hundred meters.

Oh!

Hala: Wow!

No!

What is that?

Steve, voice-over: And the cave still has more secrets.

Steve: That's utterly extraordinary.

Hala: Wow.

It's a male ibex.

A mountain goat.

It's not usual for mountain goats to go into caves, certainly not deep into them.

But it's so perfect.

Yes.

Every single vertebrae is in perfect form.

Ahh.

That's not a rock.

That's dung.

That's his--that's his intestine.

That's what the-- that's part of its stomach, like its rumen.

[Gasps] So essentially, that is its last few meals desiccated.

That is where the internal organs would have been.

Ohh.

It... That is so perfect.

It's like a museum specimen underground.

How old do you think that could be?

[Sighs] So... they're not found in this area anymore.

They're extinct where we are right now.

Mahmoud: Oh, the ibex.

[Speaks Arabic] Do you know when the Arabian ibex disappeared from this area?

Uh, if you ask the people here, they said around 100 years before.

Oh, a hundred years before.

Yeah.

So it's been here for at least that long.

Possibly--possibly more.

Oh, hang on!

There's one right here.

Look!

Look at this.

There's a female.

But this one is smashed up.

This one is very broken.

Aldo: Whoa, Steve.

There's another one there.

Look at that.

So now we have the remnants of 3 ibex in here, one perfectly preserved, two pretty smashed up.

But a long time ago.

Hundreds, possibly over a thousand years ago.

♪ Steve, voice-over: 3 kilometers into the lava tube, and we've added 3 incredible animal species to our discoveries.

♪ Steve: The tunnel's starting to narrow.

Mm-hmm.

I think it's closing.

Steve, voice-over: We haven't broken the 3.3 kilometer record.

Ahh.

It is closing.

And it's not looking likely.

♪ I think this is it, guys.

I think this is the end.

This is the end, yeah.

Oh, actually, no.

Hala: Ohh!

Steve, voice-over: There is a way through.

Steve: Don't come below me here.

It's very, very slippy.

♪ It wouldn't take much more of a slip there to completely block this off.

♪ If it collapsed any further, then we would be stuck in here.

♪ And it would take a long time for someone to find us.

Steve Backshall in about a thousand years' time will come and find our bones.

♪ This bag, medic kit, OK?

Pass you the stretcher, OK?

Steve, voice-over: It's past our agreed return time, so Justin's heading into the cave to find us.

Justin: OK, Nessar?

Nessar: Yes?

I will move very quick, so you go along the top, yes?

♪ Justin: OK, mainly radio check.

I am just below the sinkhole, cave two.

Woman on radio: Great.

Hearing you loud and clear.

Good luck.

Over.

♪ OK, thank you.

Uh, latest 6:00.

♪ Ahh, that's it.

Aldo: Is that the end of the road?

Looks like it.

Nope, that's... the deadest of dead ends you'll ever find.

So that's that.

So, Mahmoud, do you have the--do you have the length?

3.6 kilometers.

3.6 kilometers.

[All cheering] Steve, voice-over: At 3.6 kilometers, this is the longest lava tube... Saudi Arabia!

ever discovered on the Arabian Peninsula.

I want to say that thank you guys for being with us in Saudi Arabia in Harrat Khaybar, in this cave, which we are going to call it together [Speaking Arabic], means the Father of Ibex.

Ohh!

I love it.

Yes, the Father of Ibex, because we have seen some of those big ibex inside.

And hopefully, we shall bring people who are going to analyze all this stuff and give us the exact ages, and we will inform you about it.

That's amazing.

That is such amazing news.

Let's go.

Let's go.

[Speaking Arabic] ♪ Steve, voice-over: What we've discovered in the Father of Ibex Cave offers us snapshots back in time, all evidence that will help scientists better understand the relationship between humans and this landscape through the ages.

[Whistle blows] [Whistle blows] [Whistle blows] [Whistle blows] Justin: Yo!

♪ Aldo, I've got you.

Aldo on radio: Hey, man.

We are all good, all set.

We're walking back.

We'll be in the sinkhole probably fairly soon.

Over.

OK, I am inside the cave.

I can see your light.

Steve, voice-over: Together with Mahmoud and Hala, we've discovered the longest lava tube on the Arabian Peninsula.

But that's not all.

Steve: The lava tubes themself, as an environment that is sealed off in time, offers a window back through prehistory covering tens of thousands of years of change and evolution here on the Arabian Peninsula.

They are little microcosms, little magnifying glasses on what is so special about this part of the world.

Natural history, anthropology, history, everything is frozen in time inside those remarkable places.

Steve, voice-over: As Saudi Arabia becomes more accessible to the rest of the world, these underground pockets of history could give up yet more of their secrets, teaching us more about where we came from, who we are, and what our future could hold.

Announcer: "Expedition with Steve Backshall" is available on Amazon Prime Video.

♪