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".
Thiên Đường Cave
Thiên Đường Cave (Paradise Cave) is a cave in Phong Nha-Kẻ Bàng National Park, UNESCO's World Heritage Site, 60 km northwest of Đồng Hới city.
Thiên Đường Cave is located on an elevation of 200 meters above the sea level, near the west branch of Ho Chi Minh Highway, in Son Trach Commune, Bố Trạch District, Quảng Bình Province, Vietnam. The cave was discovered by a local man in 2005 and the first 5 km of this cave was explored by explorers from British Cave Research Association in 2005, the whole 31 km was explored and publicly announced by the British cave explorers. This cave is 31 km long, longer than Phong Nha Cave which had been considered the longest cave in this national park. The height can reach to 72 m and 150 m wide. The limestone formation is also more spectacular than that of Phong Nha Cave. The British cave explorers were impressed by the beautiful and spectacular stalactites and stalagmites inside this cave and they named it "Thiên Đường Cave" ("Paradise Cave").
In 2012, a new species of troglobiontic scorpion species, "Vietbocap thienduongensis" was found in here.