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".
Oudomxay Province
Chom Ong Cave, the longest cave in Laos, is located in Ban Chom Ong, 45 km to the northwest of Oudomxay town and is the biggest known cave in northern Laos. The cave was explored by a team of cave researchers during 2009, 2010 and 2011 and reported to be 18.4 km long and considered as the second longest in Laos and 9th longest in South East Asia. The average dimensions of the cave is 20–25 m in width and 20–30 m in height. It has two passages, one is a stream and the other has fossils and both connect to a large hall which is 100 m long, 30 m wide and of varying height of 30–50 m up to the roof. It has a stream inlet in the north and the stream outflows in the southern end.