Velebit caves
The "Lukina jama" cave is 1431 m deep (2013), the deepest cave in Croatia, 14th deepest cave in the world and the deepest cave in southeast Europe. At its foot, there are ponds and streams including one of the largest known colonies of subterranean leeches ("Erpobdella mestrovi"), which has been ascertained to represent a new species, genus and also family. Other species discovered in the system, include the air-breathing land snails "Zospeum tholussum". Like Lukina jama, Slovacka jama, Velebita and Meduza are also located at the "Hajdučki i Rožanski kukovi" special reserve, a dedicated part of the Sjeverni Velebit national park.
Dent de Crolles
The réseau de la Dent de Crolles, which lies beneath the summit plateau, is one of the most complex and longest cave systems in Europe, and is considered to be one of the birth places of modern caving. Its first detailed exploration was during World War II by a small team of French cavers which included Pierre Chevalier, Fernand Petzl, and Charles Petit-Didier. Their explorations saw it become the deepest cave in the world at the time with a depth of . The lack of available equipment during the war forced Pierre Chevalier and the rest of the team to develop their own equipment, leading to technical innovation. The first use of the single rope technique with prusik and mechanical rope-ascenders (Henri Brenot's "monkeys", first used by Chevalier and Brenot in a cave in 1934) can be directly associated with its exploration.