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.
Caverna de Santana
Discovered and described at the beginning of the twentieth century as "Caverna do Rio Roncador" by the German naturalist Richard Krone, it had the potential to become one of the deepest caves in the state, but ended up being one of the most important and visited caves in the country. It is the longest cave within the state area with a horizontal projection of 8.373 meters and unevenness of 61 meters. It is widely used for environmental education tours and photography.