is the deepest-known cave on Earth.
It is located in the Arabika Massif of the Gagra Range of the Western Caucasus, in the Gagra district of Abkhazia, a breakaway region of Georgia.
The numerous caves underneath the Arabika Massif started to form several millions of year ago when the mountains began to rise. What came to be named Krubera Cave was discovered in 1960 when L. Maruashvili led other Georgian speleologists to explore the cave. Decision was made to name the cave after Russian geologist Alexander Kruber, who had carried out some field studies in the Arabika area about four decades earlier. The exploration was, however, abandoned after the speleologists got to a depth of 95 meters due to passages that were too narrow and hard to negotiate. Except for occasional visits by cavers, Krubera Cave was virtually abandoned for the next two decades.
Krubera Cave has an extremely steep profile and reveals a huge thickness of the vadose zone. The lower boundary of the vadose zone (the top of the phreatic zone) is at an elevation of about 110 m (360 ft) at low flow, which suggests a low overall hydraulic gradient of 0.007-0.008. Low-TDS groundwater is tapped by boreholes in the shore area at depths of 40–280, 500, 1,750, and 2,250 m below sea level, which suggests the existence of a deep flow system with vigorous flow. Submarine discharge along the Arabika coast is reported at depths up to ~400 m b.s.l.
Krubera Cave branches into two at a depth of 200 meters. One of these branches, Kuybyshevskaya, has been explored to a depth of 1,293 meters, while the main branch has been explored further deep down. It was in 2001 that Krubera Cave attained the status of the deepest cave in the world. The Ukrainian Speleological Association was able to reach a depth of 1,710 meters into the cave in that year, thereby supplanting Lamprechtsofen cave in the Austrian Alps as the deepest.