Krubera Cave
The difference in elevation of the cave's entrance and its deepest explored point is . It became the deepest-known cave in the world in 2001 when the expedition of the Ukrainian Speleological Association reached a depth of which exceeded the depth of the previous deepest-known cave, Lamprechtsofen, in the Austrian Alps, by . In 2004, for the first time in the history of speleology, the Ukrainian Speleological Association expedition reached a depth greater than , and explored the cave to . Ukrainian diver Gennadiy Samokhin extended the cave by diving in the terminal sump to 46 metres' depth in 2007 and then to 52 m in 2012, setting successive world records of 2,191 m and 2,197 m, respectively. Krubera is one of the two known caves on Earth deeper than 2,000 metres.
Pettyjohn Cave
Pettyjohn Cave (also known as Wilsons Cave, Pettyjohn's Cave, Petty John's Cave, and other similar spellings) is a karst cave located in Walker County, Georgia on the east side Pigeon Mountain in the Appalachian Plateau of Northwest Georgia. It has a surveyed length of 31,490 ft and reaches a depth of 235 ft. The cave is accessible via a path from a gravel parking area on the side of Rocky Lane. Out of the 242 listed, it is 119th longest cave in the United States as declared by the Georgia Speleological Survey.