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".
Pettyjohn Cave
Pettyjohn Cave (also known as Wilsons Cave, Pettyjohn's Cave, Petty John's Cave, and other similar spellings) is a karst cave located in Walker County, Georgia on the east side Pigeon Mountain in the Appalachian Plateau of Northwest Georgia. It has a surveyed length of 31,490 ft and reaches a depth of 235 ft. The cave is accessible via a path from a gravel parking area on the side of Rocky Lane. Out of the 242 listed, it is 119th longest cave in the United States as declared by the Georgia Speleological Survey.