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".
Cades Cove
The fracturing and weathering of the limestone and sandstone in Cades Cove has led to the formation of several caves in the vicinity, the two largest of which are Gregory's Cave and Bull Cave. Bull Cave, at 924 feet (281 m), is the deepest cave in Tennessee. Trilobite and brachiopod fossils have been found in Gregory's Cave.