Postojna Cave
The cave was first described in the 17th century by Janez Vajkard Valvasor, and following the discovery of a new area of the cave in 1818 by local Luka Čeč it was opened to the public in 1819. A tourist railway was added in the 1870s and electric lighting in 1884. The tourist railway cars were initially pushed along by the guides themselves, but in the early years of the 20th century a gas locomotive was introduced. After 1945 this was replaced by an electric one. Today 5.3 kilometres of the caves are open to the public, the longest publicly-accessible depth of any cave system in the world.
The caves are also home to the endemic olm (proteus anguinus), the largest trogloditic amphibian in the world. Part of the tour through the caves includes a pool with some olms in it, making this the only place in the world where the olm can be seen by tourists.
See also Predjama Castle.