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.
Oudomxay Province
Chom Ong Cave, the longest cave in Laos, is located in Ban Chom Ong, 45 km to the northwest of Oudomxay town and is the biggest known cave in northern Laos. The cave was explored by a team of cave researchers during 2009, 2010 and 2011 and reported to be 18.4 km long and considered as the second longest in Laos and 9th longest in South East Asia. The average dimensions of the cave is 20–25 m in width and 20–30 m in height. It has two passages, one is a stream and the other has fossils and both connect to a large hall which is 100 m long, 30 m wide and of varying height of 30–50 m up to the roof. It has a stream inlet in the north and the stream outflows in the southern end.