The most famous and frequently visited is the Postojna Cave, first mentioned in 1213. With more than 26 million visitors so far it has been the most visited cave in Europe. There are about five kilometres of regulated passages out of a total of 21 kilometres. Visitors are taken for a tour of the cave which is full of shining stalagmites and stalactities of different colours and shapes and little lakes with clear water by a special electric train. The main attraction of the Cave is the human fish, proteus anguinus.