The Postojna Cave system is a network of caves over 24km in length cut into the karst rock by the Pikva river. It has been a tourist attraction since 1819 when the Austrian emperor Francis I visited. There has been a railway to visit the caves since the nineteenth century. It is the second longest cave system in Slovenia and I believe the longest cave tourist trail in the world.
In the cave system we can also find olms (also known as proteus (Proteus anguinus)), a fully aquatic salamander. Unlike most amphibians, the olm spends all of its life underwater. Ift is found in the karst cave systems in the Dinaric Alps in what was western Yugoslavia. It was first mentioned in 1689 by the local naturalist Valvasor in his Glory of the Duchy of Carniola, who reported that, after heavy rains, the olms were washed up from the underground waters and were believed by local people to be a cave dragon's offspring. This animal has adapted to living in complete darkness. It is blind but has very good senses of smell and hearing.