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".
Coral Cave
The Coral Cave () is a marble cave at the northernmost tip of Jämtland, near Ankarvattnet, Sweden. It was discovered in 1985. So far, six kilometres of it have been explored, making it Sweden's longest cave. Members of the public are not allowed to visit the Coral Cave without a guide.