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.
Gap Cave
Gap Cave is located just underneath Pinnacle Overlook in the Cumberland Gap National Historical Park, Lee County, Virginia. Currently, the cave has a surveyed length of 18.5 miles and is the 42nd longest cave in the United States and 154th in the world. There are six known entrances: the Gap Cave Entrance (also known as the King Solomons Cave Entrance), an artificial entrance, known as the Cudjo's Cave Entrance, the Stream Entrance, the Soldiers Cave Entrance, the Big Saltpeter Cave Entrance, and the Wellhole. All lead into the same cave, Gap Cave.