One of the world's deepest and most dangerous caves lies in Abkhazia, a disputed part of Georgia. It takes days to get to the ...

Krubera Cave in the republic of Georgia is currently the deepest known cave, at 7,208 feet. But Dark Star, with so many areas still to survey, is a prime candidate to take over the title.

Sunlight penetrates deep inside, allowing mosses ... shafts—tunnels that slope relatively straightforwardly down—natural caves are nonlinear and ex-pand and contract according to the movement ...

But these deep, dark habitats are often challenging for humans to access. Underwater caves can be dangerous for even the most experienced divers. There is usually no natural light, spaces can be ...