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.
Bill Steele (cave explorer)
Continuing to explore caves throughout the United States, Steele led and participated in expeditions to Sistema Huautla in Mexico almost every year through the 1980s. In 1987, the Huautla expedition connected the deep cave Nita Nanta to Sistema Huautla; which established it as the second deepest cave in the world. Steele went to Kijahe Xontjoa on the plateau to the east of Huautla with an expedition of Swiss explorers in 1993, and explored depths over 1,000 meters.