Velebit
There are hundreds of "holes" on Velebit. It has the largest and deepest caves in Croatia. The three-part "Lukina jama" cave is 1392 m deep, making it one of the deepest caves in the world, and the deepest in southeast Europe, while the "Slovačka jama" is 1320 m. What makes it unique is that it is completely vertical, steepest in the world. At the bottom of the pothole is a water course or siphon with branches that are still unexplored. A kind of leech was discovered in the pothole, which has been ascertained to represent a new species, genus and family; it has been named "Erpobdella mestrovi".
Pit cave
During World War II, a team composed by Pierre Chevalier, Fernand Petzl, Charles Petit-Didier and others explored the Dent de Crolles cave system near Grenoble, France. It became known as the deepest cave in the world () at that time. The lack of available technical equipment during the war forced Chevalier and his team to innovate and develop their own. The scaling-pole (1940), nylon ropes (1942), use of explosives in caves (1947), and mechanical rope-ascenders (Henri Brenot's "monkeys", first used by Chevalier and Brenot in a cave in 1934) can be traced historically to the exploration of the Dent de Crolles cave system.