At 2,197 meters (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 kilometers (8,346 miles.) I would love to get inside, but I know the fear would paralyze me. I love to go through its complete (so far) map, though.
Probably the scariest fact is this:
Ukrainian diver Gennadiy Samokhin extended the cave by diving in the terminal sump to 46 m depth in 2007 and then to 52 m in 2012, setting successive world records of 2,191 m and 2,197 m respectively. Krubera remains the only known cave on Earth deeper than 2,000 meters.
Imagine that. Dive into the "terminal sump" for 52 meters 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.