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".
Mount Adams (Washington)
In the area surrounding Mount Adams, many caves have formed around inactive lava vents. These caves are usually close to the surface and can be hundreds of feet deep and wide. A few of the more well known caves include the Cheese Cave, Ice Cave, and Deadhorse Caves. Cheese Cave has the largest bore of the caves near Adams with a diameter of and a length of over . Ice cave, which is made up of several sections created by several sinkholes, has an ice section that is long and in diameter and noted for its ice formations. From the same entrance, the tube continues another to the west. Deadhorse Cave is a massive network of lava tubes. It the most complex lava tube in the United States with of passage. These caves are all just outside of Trout Lake. These and many other caves in the Trout Lake area were at one time part of a huge system that originated at the Indian Heaven volcanic field. The most obscure caves around Adams are the Windholes on the southeast side near Island Cabin Campground.