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".
Chevé Cave
Chevé Cave was discovered in the mid-1980s by Bill Farr and Carol Vesely. Since then it has been pushed to the depth of , making it the second deepest cave in the Americas. The cave system has the greatest proven depth potential in the world as proven by a dye trace from its main entrance to the resurgence 2547 meters lower. The current terminus of the main Chevé system is a large breakdown pile reached after diving through two sumps. It is just over 9 kilometers from the entrance, making it currently one of the most remote underground locations on earth. Due to the logistical difficulties of continuing exploration from this point, current expeditions are focusing on finding mid-way entrances that might provide a quicker route into the middle Chevé system.