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".
Caverna de Santana
Discovered and described at the beginning of the twentieth century as "Caverna do Rio Roncador" by the German naturalist Richard Krone, it had the potential to become one of the deepest caves in the state, but ended up being one of the most important and visited caves in the country. It is the longest cave within the state area with a horizontal projection of 8.373 meters and unevenness of 61 meters. It is widely used for environmental education tours and photography.