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".
John Volanthen
In 2004, Volanthen and Stanton set a world record for the greatest depth achieved in a British cave, cave diving at Wookey Hole in Somerset.
In 2010, Volanthen, Stanton, Jason Mallinson, and René Houben set a world record for the longest cave penetration dive, reaching in the Pozo Azul cave system in the Rudrón Valley in Spain.