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".
Bill Steele (cave explorer)
Charles William Steele, Jr. (born October 17, 1948), known as “Bill Steele,” is a cave explorer. He is a speleologist who has led and participated in expeditions to many of the longest and deepest caves in the USA, Mexico, and China. He has explored more than 2,500 caves across North America and Asia and has written two books chronicling his expeditions: "Yochib: The River Cave", and "Huautla: Thirty Years in One of the World's Deepest Caves.” TV shows such as National Geographic Explorer, NOVA and How’d They Do That? have aired programs on his expeditions.