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".
Ellison's Cave
Ellison's features a number of underground vertical pitches including the two deepest pits in the continental United States: Fantastic (586 feet) and Incredible (440 feet). These two pits lie on opposite sides of the cave. Nearby and parallel to Fantastic are Smokey I (500 feet), Smokey II (262 feet), and other extremely deep pitches. There are over 7 routes to reach the bottom level of the cave from the Fantastic side. Fantastic and Smokey I both extend to TAG Hall, a passage at the bottom of the cave. To reach Fantastic, or the large pits on the Fantastic side, cavers must also descend the Warm Up pit (125 feet).