The Velebit mountains of Croatia have several deep caves with some of the world's largest subterranean vertical drops.

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.^[1] 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.^[1] Other species discovered in the system, include the air-breathing land snails Zospeum tholussum.^[2] 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.

Other notable caves include the "Slovacka jama" (Slovak pit), (1,320 m deep), "Velebita" (1026 m deep with underground free fall vertical drop of 513 metres ) and "Meduza" (679 m deep).

The vertical shaft "Patkov Gušt", named after a deceased Croatian speleologist^[3] is 553 meters deep and the second deepest pitch in the world as of 2007^[update].