The video above is proof that a whole world can thrive underground. Captured by Beijing-based travel photographer, Ryan Deboodt, using a GoPro-carrying drone, the footage provides a rare view into the gigantic Hang Son Doong cave in Vietnam - and there's an entire rainforest ecosystem just waiting to be explored.
The cave was first discovered in 1991, but only explored for the first time in 2009 by a team of scientists from the British Cave Research Association. What they found was that the limestone cave was far bigger than expected. So big, in fact, that it's the biggest known cave in the world, with its largest chamber measuring more than 5 km long, 200 metres high and 150 metres wide. The cave also contains some of the tallest known stalagmites in the world, which are up to 70 m tall. That's like... a 20-storey building.
Obviously it's pretty hard to get aerial shots of an underground world - just imagine flying a helicopter in there - but Deboodt managed to do just that using a drone. The video was filmed near the entrance of the first and second skylights of the cave, which are 2.5 and 3.5 km inside the cave respectively, as Deboodt writes on his Vimeo page.
The result is pretty damn other-wordly, showing forests, hills, cliff-faces, streams and stone ridges, all buried deep underground. Look closely and you can see people exploring the jungle and rocky outcrops of the cave, dwarfed to the size of ants by the sheer scale of the cavern.
The cave even has its own climate system, and you can see mist rising off the forests in the footage. We don't see any traces of solid clouds in this video, but the smaller Er Wang Dong cave system in southwest China has its own weather, and we imagine Hang Son Doong is pretty similar.
In fact, the footage above even makes the thought of living inside a cave somewhat palatable and un-claustrophobic. We've now got a new ideal spot to run to if a zombie apocalypse breaks out. Watch it and enjoy,and check out the BBC How To Grow a Planet footage below for a more up-close look.