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".
Indian Caverns
Indian Caverns was a show cave in Spruce Creek, Pennsylvania, United States from 1929-2017. It is a horizontal karst cave of Ordovician Nealmont/Benner limestone, estimated to be about 500,000 years old. It is the second-largest cave in Pennsylvania and the largest limestone cave. Indian Caverns consists of two sections, originally separated by a 14-foot wall: the "Historic Cave" and the "Giant's Hall". The "historic" part of the cave is generally low-ceilinged and closer to the surface (as shallow as 15 ft) with a couple of wide rooms and extensive speleothem formation. The Giant's Hall area consists of several large passageways, up to 60 feet high, but with fewer speleothems - though it does include the largest sheet of flowstone in the northeast and a substantial rimstone pool. The lowest point of the cave is approximately 140 feet beneath the surface and the cave temperature is a constant 56 degrees Fahrenheit (13 degrees Celsius).