The Postojna Caves, one of Slovenia's most spectacular natural sights, consist of a 27-kilometre underground system of passages, tunnels, galleries and chambers with wonderful dripstones.
The caves, also famous for providing a home to the olm (Proteus anguinus), an amphibian salamander endemic to subterranean waters of southern Europe, can be viewed from a small cave train.
Predjama Castle, part of which is built into a 123-metre high vertical cliff face, was originally known as the home of the legendary 15th-century rebellious knight Erasmus. After coming into conflict with the imperial court in Vienna, Erasmus shut himself in the castle and resisted an Austrian siege for a very long time. The castle, which assumed its present Renaissance appearance in the 16th century, now houses a museum.