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".
Gourgouthakas
Gourgouthakas (; from "small cutting on rocks, in which rain water is collected and from which animals drink water") is a cave located in the Lefka Ori mountains on the Greek island of Crete. It is the deepest cave in Greece, with an explored depth of , and is the 43rd deepest in the world.