Škocjan Caves, the first Slovenian location inscribed on the Unesco World Heritage list, is considered the largest underground canyon in Europe. Inside it flows the Reka, the largest Slovenian sinking river. Considered the birthplace of modern speleology, the river is also home to Europe's most rare and valuable species. For instance the olm, also called human fish, a curious animal that can live 100 years, up to 10 without food, and can grow back parts of its body.