The Pivka and Black Caves are also part of the Postojna cave system. The Pivka cave offers a magnificent insight into the subterranean riverbed of the Pivka River and is also the only location of the cave system which allows visitors to observe the underground water passages. A walk through the cave sheds light on the mysteries of the formation of subterranean passages and is a wonderful monument to the power of water. Through an artificial passage, visitors can access the Black cave, where thousands of tiny crystals glitter marvellously, making the cave come alive with magic.

The Otok Cave lies about a kilometre from the Postojna Cave, and is part of the former common Postojna cave system. It is an attractive tourist destination, and has also been visited and depicted by Slovenian and foreign filmmakers due to its unique beauty. The cave is 623 metres long.

The Križna Cave is a world famous karst cave. It is noted for its 47 subterranean lakes, and the discovery of cave bear bones. The one hour tour of the dry part of the cave and a boat ride around the first lake is intended for larger groups, while the four-hour tour including a boat ride across 13 lakes will accommodate up to four persons at most.

The Planina Cave is the largest water cave in Slovenia. It is adorned with precipitous chambers, narrow passages, subterranean lakes, rapids, siphons, and numerous cave formations. The cave is also the location of a true rarity-the confluence of two underground rivers. The River Pivka, flowing from the Postojna basin, and the River Raka, which flows through the areas of Rakov Škocjan, Cerknica plain, and Javornik. The part of the cave intended for tourists measures 900 metres and can be visited regardless of the weather and water level, while other parts of the cave can only be accessed when the water level is low and by using special equipment. When the water level is low, boat tours lasting up to six hours can be arranged. Halogen lamps are included in the cave tour. A tour lasts approx. 1.5h.

The Postojna Cave is a system of 20 kilometres of passages, galleries, and chambers, which have been visited by over 33 million visitors accompanied by experienced guides over almost two hundred years. At the same time it is the largest Classical Karst cave and the most visited cave in Europe. Already in 1872, railway tracks were installed in the cave, and in 1884, electricity was also installed. Today, visitors can satisfy their curiosity by learning about the origin of the caves, by examining the passages and chambers, and especially by observing the rising stalagmites or hanging stalactites, the joining columns, the creasing curtains, and the strings of endless fantastic shapes. The cave is easily accessible and has no steps or steep inclines; part of the cave is viewed from the train, and the rest can be observed on foot. The Postojna Cave is also considered the birthplace of speleobiology. The Postojna-Planina cave system is the home of as many as 85 completely adapted animal species, making it the world’s largest cave ecosystem, and the crown jewel of biological diversity. The most famous inhabitant is of course the olm, or the human fish (Proteus anguinus).

The Cave below Predjama Castle can be accessed via one of three routes. The most well known is the Stable route, where traces from the Late Stone and Copper Age, as well as the Roman Era, were discovered. This route into the underworld leads to the Main Passage. In the Passage of Names, signatures of visitors from as early as the 16th century can be seen, making it a notable attraction and a must-see landmark. The Passage of Names connects the Main Passage to the Fiženica, which can be accessed from above the castle and descend 600 metres into the underworld. Its position and favourable temperature have made this cave a popular refuge for endangered bats-for this reason, the cave is off limits during the bats’ winter hibernation period.