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)
Charles William Steele, Jr. (born October 17, 1948), known as “Bill Steele,” is a cave explorer. He is a speleologist who has led and participated in expeditions to many of the longest and deepest caves in the USA, Mexico, and China. He has explored more than 2,500 caves across North America and Asia and has written two books chronicling his expeditions: "Yochib: The River Cave", and "Huautla: Thirty Years in One of the World's Deepest Caves.” TV shows such as National Geographic Explorer, NOVA and How’d They Do That? have aired programs on his expeditions.