Veryovkina Cave, the deepest known cave on Earth ... The air pressure is 10% higher than at the surface, and temperatures hover at a frigid 39°F (4°C), making hypothermia a constant danger.

Probing a series of “windows” in the walls of the deepest part of the cave, the team was blocked time and again by sumps or impossibly tight squeezes. But finally, on October 19, Kasjan ...

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.