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".
Tears of the Turtle Cave
The entrance to Tears of the Turtle Cave was found in 2006. The cave passage is mostly a two to three foot wide fissure that follows a stream downward through numerous rappels. In 2014 a team of nine cavers explored new passage pushing the cave to a depth of 1629 feet and in doing so passed New Mexico's Lechuguilla Cave to become the deepest known limestone cave in the United States. Exploration continued in 2016 when teams returned to push the cave to its current known depth of 1659 feet. On those trips the difficulty necessitated establishing camp in the cave for the first time. This, along with the technical rope work, 39 degree temperature, and remote location of the cave make continued exploration difficult. A return trip is currently planned for 2019.