The cave Postojnska Jama was opened as a tour cave in 1819. Although the Postojnska Jama is primarily a show cave, it plays an important role in the history of cave sciences. The pioneer natural science researcher Valvasor investigated Postojnska Jama in 1689. The first exemples of cave fauna were discovered by Proteus in 1797. Postojnska jama is often called the cradle of speleobiology. This cave is the longest cave in Slovenia, contains spetacular formations, and can be toured via an underground train.