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.
North West Highlands Geopark
The area contains a number of limestone caves. The most well known of these is Smoo Cave, a large sea cave near Durness. This cave is unique within the UK in that its outer chamber was formed by the action of seawater, while the inner chambers were formed by fresh water. Its entrance 15 metres high, is the largest entrance of any sea cave in the British Isles. Archaeological excavations have found evidence of human habitation dating back to the Mesolithic period. The cave became well known after Sir Walter Scott visited it in 1814. Another notable cave site is the Inchnadamph Bone Caves. At these caves, remains of Eurasian lynx, brown bear, Arctic fox, reindeer and polar bears have been found; as well as human remains dated between 4,515 and 4,720 years old. Uamh an Claonaite, Scotland's longest cave is partly located below these Bone Caves.