If you're claustrophobic, look away now - a pair of particularly adventurous YouTubers have showed just how deep some caves can go.
ActionAdventureTwins are identical twins who love spelunking, or cave exploration, and post loads of videos on YouTube showcasing their passion.
In one video from late 2022, they ventured to one of the deepest caves in the United States: the Fantastic Pit, in Ellison's Cave in the state of Georgia.
It's the deepest unobstructed underground pit in the whole country, and you can pretty immediately see why as they start to delve into it.
The first section of the exploration involves a direct drop of 128 feet which they complete by shimmying down a rope (secured by safety equipment). Once they reach a little shelf down there, it's time for the real experiment - tying a GoPro action camera to the end of a rope and seeing how far down they can drop it.
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They have enough slack to get it down a further 528 feet to the bottom of the cave - a pretty crazy distance.
The system they use to actually lower and then retrieve the camera is impressively simple, too - they have a hand drill with the line twined around it.
By spinning the drill in either direction, they can lower or raise the camera, which works brilliantly.
A small spotlight mounted on the GoPro lights up its surroundings, and the further it goes the eerier the footage becomes.
You can see enormous shelves of rock surrounding the pit as the camera spins around, before it eventually reaches the floor of the cave.
This seems to be a surprisingly flat and clear floor, littered with small rocks but with an amazingly open amount of space, too. You can clearly hear a waterfall in the darkness somewhere, too.
After showing this off a little, the camera begins its slow ascent back into the brothers' hands.
Viewers have pretty much unanimously commented on how weird and creepy that footage ended up being, showing off the sorts of depths that few humans would have ever seen in person.
One commenter wrote: "This is the stuff in my nightmares but for some reason I'm addicted to watching it."
Another theorized about why the cave looked how it did: "Honestly surprised the bottom wasn't full of water. It must drain out somewhere even deeper. It would be fun to explore it with a drone if you could."
Finally, one other person with a potentially more fragile constitution said: "The muffled descending sound was terrifying! And the spinning... I was just waiting for something to jump scare me."
The section of the video where the camera is spinning as it descends is indeed pretty disorientating, so you can only imagine how freaky it would be to actually be in the cave.