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".
Tuckaleechee Caverns
Tuckaleechee Caverns () is a set of caverns and AAA GEM attraction in Townsend, Tennessee, near the Smoky Mountains. The caverns were discovered in the mid-19th century and were opened to the public by Bill Vananda and Harry Myers in 1953. The caverns are known for the "Big Room", an immense cave/cavern room that a football stadium could fit inside. The caverns have stalagmites reaching 24 feet tall with flow-stone formations hundreds of feet in length and width.
Open MARCH 15 to NOVEMBER 15
Tuckaleechee Caverns also has the tallest underground waterfall in the country named "Silver Falls", a 210-foot two-tier waterfall. The cavern originates at White Oak Sinks in the Great Smoky Mountains National Park. The Caverns host a seismograph system monitored by the United States Department of Defense,CTBTO and the United States Geological Survey (USGS).