At 2,197 metres (7,208 feet) the Krubera cave is the deepest on Earth. Located in the Arabika Massif, of the Western Caucasus in Abkhazia, Georgia, it extends for 13,432 kilometres (8,346 miles). I would love to get inside, but I know the fear would paralyse me. Going through its complete (so far) map is fascinating.
Probably the scariest fact is this:
Ukrainian diver Gennadiy Samokhin extended the cave by diving in the terminal sump to 46 metres depth in 2007 and then to 52 metres in 2012, setting successive world records of 2,191 metres and 2,197 metres respectively. Krubera remains the only known cave on Earth deeper than 2,000 metres.
Imagine that: diving into the "terminal sump" for 52 metres more. I know that there's probably nothing big living in there (something small is), but if there are any monsters hiding somewhere in this world, it has to be in one of these caves.