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.
Neffs Cave
In 1952 the Salt Lake Grotto of the National Speleological Society was established, and several weeks later the grotto's members obtained permission from the National Forest Service to explore the cave. They spent nearly eleven hours in the cave but had not reached the end of the main passage before they had to turn back. Teams from the grotto returned in 1953 and 1956, and in the last visit they succeeded in reaching the bottom of the main passage. They calculated a vertical depth of 1186 feet (361 meters), which was later revised to the present figure of 1163 feet (354 meters). Neffs Cave is the 13th deepest cave discovered in the United States.