What's the deepest cave?
Krubera Cave
Krubera Cave (Georgian:კრუბერის გამოქვაბული or კრუბერის ღრმული, translit.:k'ruberis gamokvabuli or k'ruberis ghrmuli; Also known as Voronya Cave, sometimes spelled Voronja Cave) is the second deepest known cave on Earth after the Veryovkina Cave. It is located in the Arabika Massif of the Gagra Range of the Western Caucasus, in the Gagra district of Abkhazia,[note 1] a breakaway region of Georgia, currently under Russian occupation.[1][2]
Cave diving
Silfra is a fissure between the North American and Eurasian tectonic plates in Thingvellir National Park. It is the only place in the world where you can dive or snorkel directly in a crack between two tectonic plates. The tunnel from the entrance of Silfra to the cave is commonly known as ‘The Tunnel’, due to the strong current that ‘flushes’ divers attempting to swim through. This tunnel is rarely dived due to the dangerous head-first vertical dive needed to pass through. The deepest part of the cave is at least deep, and has only been dived by a few people because of the narrow and unstable passages. 