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.
Mount Adams (Washington)
In the area surrounding Mount Adams, many caves have formed around inactive lava vents. These caves are usually close to the surface and can be hundreds of feet deep and wide. A few of the more well known caves include the Cheese Cave, Ice Cave, and Deadhorse Caves. Cheese Cave has the largest bore of the caves near Adams with a diameter of and a length of over . Ice cave, which is made up of several sections created by several sinkholes, has an ice section that is long and in diameter and noted for its ice formations. From the same entrance, the tube continues another to the west. Deadhorse Cave is a massive network of lava tubes. It the most complex lava tube in the United States with of passage. These caves are all just outside of Trout Lake. These and many other caves in the Trout Lake area were at one time part of a huge system that originated at the Indian Heaven volcanic field. The most obscure caves around Adams are the Windholes on the southeast side near Island Cabin Campground.