Things to Do in Postojna, Slovenia

Quick facts: The formations in the cave reach gigantic sizes. Some stalactites measure up to 10 meters. The tour includes a 3.7-kilometer underground train ride that fascinates thousands of visitors every year.

Highlights: During the tour, you can see the proteus anguinus, the blind salamander that inhabits its underground waters and is a symbol of Slovenian biodiversity. The cave has a system of galleries and passages that add up to more than 24 kilometers, but only 5 are open to the public.

Quick facts: It nests at the mouth of a cave more than 123 meters deep. It has a secret tunnel system historically used for escape or to receive supplies during sieges.

Highlights: Its location embedded in a 123-meter cliff offers impressive views and a unique atmosphere. On its walls, there is an original catapult that can still be seen in operation during guided tours.

Quick facts: This park houses a cave with more than 24 kilometers of underground galleries open to the public. An electric train takes visitors through dark tunnels with ancient stalactite and stalagmite formations.

Highlights: The cave has a natural underground amphitheater with a capacity of 10,000 people, where concerts are held with perfect echo. Also, you can see the olm, a peculiar blind salamander that lives only in these underground waters.

Quick facts: The underground train transports visitors along 2.5 kilometers inside one of the longest caves in Europe. More than 1.2 million people travel this route each year, experiencing a unique journey underground.

Highlights: The tour includes a tunnel where the train stops to listen to the echo produced when clapping; the cave is dotted with stalactites and stalagmites that shine with strategic lights, creating impressive lighting effects.

Quick facts: An 18-square-kilometer bowl of flat karst meadow, it can transform into a temporary lake within hours when the Unica River swells after heavy rain. Water levels have been documented rising more than 20 meters in a single storm, yet the basin drains so efficiently through its ponor openings that livestock can graze here again weeks later.

Highlights: Stand at the flooded edge on a calm evening and you will see fish cruising between fence posts, a surreal sight where pasture fences become submerged breakwaters. Locals read the springs as a flood gauge: when the water turns milky white after a storm, they know the basin will fill within hours and move livestock uphill.

Quick facts: An old cave ceiling collapse left behind a 2-kilometer-long gorge where the Rak stream now flows in the open, 180 meters below the rim. Patches of water appear and vanish throughout the year, as the stream's twin lakes fill through underground passages and drain away almost overnight.

Highlights: After a few days of autumn rain, the normally dry hollows at the valley floor swell into two glowing turquoise lakes in under a day, then siphon back into the limestone just as fast. Up on the rim, a hand-built stone arch called the Devil's Bridge spans the deepest cut, while generations of locals have climbed the steep lane to the tiny chapel perched above the gorge.