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".
Nettlebed Cave
Until April 2010, when the nearby Ellis Basin cave system was found to be deeper, Nettlebed Cave was thought to be the deepest cave system in the southern hemisphere. It drops 889 metres below its upper entrance (Blizzard Pot) to its lower exit (the Pearse River resurgence), and its 24 kilometres of cave passages make it New Zealand's third longest cave.