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.
Blauhöhle
The Blauhöhle is the largest cave system in the Swabian Alps in southern Germany. The Blauhöhle presumably originated in a time when the Danube still flowed through the Blau valley. Since the shifting of the Danube, several small rivers, the Schmiech, the Ach, and the Blau, have flowed through this valley. The cave system begins about 21 meters under water at the base of the Blautopf. It continues west and northwest, rising and falling several times until after a horizontal distance of about it comes above the level of ground water and opens into the second big air-filled chamber. The maximum depth of the cave under water is .