Postojna Cave is a karst cave system located in Slovenia, near the town of Postojna. It is one of the largest cave systems in the world, with over 24 kilometers of underground tunnels, passages, and halls. The cave was formed over millions of years by the Pivka River, which still flows through it today.

Visitors to Postojna Cave can take a tour through a portion of the cave system, which includes an underground train ride and a walk through various halls and passages. The highlight of the tour is the Hall of Ceremonies, which features stunning stalactites, stalagmites, and other formations.

The cave is also home to a variety of unusual animals, including the olm, a blind salamander that can live for over a century. Visitors can see these creatures up close in a special exhibition area.

Postojna Cave is one of Slovenia's top tourist attractions, with over half a million visitors each year. It is open year-round, although hours vary depending on the season.