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".
Lechuguilla Cave
The cave was visited infrequently after mining activities ceased. However, in the 1950s, cavers heard wind roaring up from the rubble-choked cave floor. Although no route was obvious, people concluded that cave passages lay below the rubble. Led by Dave Allured, a group of cavers from the Colorado Grotto gained permission from the National Park Service and began digging in 1984. Since the breakthrough into large walking passages occurred on May 26, 1986, explorers have mapped over of passages, making Lechuguilla the eighth-longest cave in the world and fourth-longest in the United States. Lechuguilla was also the deepest known cave in the continental United States until the exploration of Tears of the Turtle Cave in 2014. Drawn by the cave's pristine condition and rare beauty, cavers come from around the world to explore and map its passages and geology.