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".
Ali-Sadr Cave
The Ali Sadr Cave (Persian: غار علی صدر) originally called Ali Saadr or Ali Saard (meaning cold) is the world's largest water cave which attracts thousands of visitors every year. It is located in Ali Sadr Kabudarahang County about 100 kilometers north of Hamadan, western Iran (more accurately at 48°18'E 35°18'N). Because of the cave's proximity to large cities such as Hamadan, it is a highly recommended destination for tourists from all corners of the world. Tours of the cave are available by pedalos.
Alisadr is the world's largest water cave, where you sit in a boat and watch the view.
This cave is located at 48°18'E 35°18'N, in the southern part of Ali Sadr village. The cave is entered at the side of a hill called Sari Ghiyeh which also includes two other caves called Sarab and Soubashi, each 7 and 11 kilometers from Ali Sadr Cave. Apparently, the water in Ali Sadr cave stems from a spring in Sarab.