|Image: overview map of the Notranjska Karst located at the entrance of Postojnska Jama.|
Notranjska is a heavily karstified triangle between the Ljubljana Basin to the north, (almost) the Gulf of Trieste to the southwest and Kvarner to the southeast. This area is also called Inner Carniola, in German Innerkrain. The administrative and economic center of the region is Postojna.
The central Notranjska Karst area is located around Postojna, Planina and Cernica. There are different definitions about what belongs to Notrjanska, some tell that it is the whole area also called Classical Karst. However, we found that the term today is used more or less for the area around Postojna, including also some nearby sights like lake Cerkniza. On the other hand there is the Classical Karst, which we define as the area around Trieste.
Notranjska has numerous important cave systems, dolines, swallow holes, seasonal lakes, and karst springs. There is a typical change between insoluble flysch lowlands and soluble limstone ridges. Rivers flow on the surface where the rock is flysch, and leave the surface, as soon as they reach the limstone. They disappear underground, just to reappear a few kilometers away behind the karst ridge.
The most famous cave system is the underground bed of the Pivka river. This cave system is enormous, more than 24km long and with numerous entrances in the whole area. In former times, when the people knew nothing about the connection of the caves, they gave every entrance its own name. Several cave entrances where developed as independent show caves. But when the caves were connected undergrond, the resulting cave had numerous names.
This area has a long speleologic history, the first known visit of the cave happened already in the 13th century. During the renaissance, in the 16th century, visitation and exploration of the cave boosted. The Postojna branch, better the upper level of Postojna Cave which is visited today, was discovered in 1818. The first light system was installed in 1818 using gas. In 1884 electric light was installed, one of the first caves in the world.
The reason is easy: the southern entrance of the cave system is really huge. The cave is big and rather easy to explore, you just walk in. And there is the history of the area. Slovenia belonged to the Austrian Hungarian Empire, an enormous multi cultural empire unique in history. So there was the possibility for famous geologists from all over Europe to visit and explore the cave.
The whole cave system of Postojna has several entrances: