The Velebit mountain of Croatia has several deep caves with some of the World's largest subterranean vertical drops. "Lukina jama" cave is 1421 m deep (2010), the deepest cave in Croatia and the deepest in southeast Europe. At its foot, there are ponds and streams including one of the largest known colonies of subterranean leeches (Croatobranchus mestrovi), which has been ascertained to represent a new species, genus and also family.
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 is 553 meters deep and the second deepest pitch in the world as of 2007.