Veternica

Veternica is a cave located on Medvednica mountain in Zagreb, Croatia. At 7,128 metres (23, 386 ft) long, with a depth of 50 metres (160 ft) and a vertical difference over 200 metres (660 ft), it is the longest known cave on its massif, and an estimated 6 km or more remain unexplored. In the 1960s, it briefly became the longest cave in Croatia. The first 380 m (1, 250 ft) is available to visitors. In 2019, it had 5787 visitors. It is an archeological site where remains of several kinds of prehistoric animals as well as humans have been found. The cave has been protected by law since 7 July 1979, with registration as a Natural Monument on 11 July of that year.

Cave data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).