The word “karst” — the geological phenomenon of limestone carved out by water — comes directly from the Slovenian “Kras”, the region in the south-west of the country. Slovenia is literally the world's birthplace of speleology. With more than 13,000 recorded caves, it is one of the most hollowed-out countries in Europe. Two caves stand out and are absolutely worth the trip.
Postojna Cave: The International Star
It is the most visited cave in Europe: 24 km of galleries, 5.3 km of which are open to the public. The visit starts with a ride on an underground train (unique in the world) that takes you into the bowels of the mountain for 10 minutes. Then comes a 1.5-hour guided walk among stalactites, stalagmites and the underground concert hall of cathedral-like proportions. The highlight: the olm (Proteus anguinus), a blind, translucent amphibian found only in the karst's underground rivers. Slovenians call it “the baby dragon”. Price: €30 adult, €18 child. Expensive, but the show is breathtaking.
Škocjan Caves: The Shock (UNESCO)
If Postojna is the star, Škocjan is the secret. A UNESCO World Heritage site since 1986, this cave is wilder, rawer, more impressive. The Martel Chamber, 146 m high, is the largest underground chamber in Europe — Notre-Dame cathedral in Paris would fit inside it. The Reka river flows 45 m below, and the Cerkvenik bridge crosses it at that height in the dark. It is dizzying. Less accessible than Postojna (no train, more steps), but the experience is incomparably more intense. Price: €20 adult. My pick if I could only see one.
Predjama Castle: The Cliff-Dwelling Eagle's Nest
Ten minutes from Postojna, Predjama Castle is built into a 123 m cliff. Constructed in the 13th century, it was the lair of the robber knight Erazem, who withstood an imperial siege for a year thanks to a secret tunnel linking the castle to the forest. You can visit the interior (armouries, cave chapel, secret passage) and the view from the cave entrance is spectacular. Price: €16, or a combo ticket with Postojna for €40.
Postojna or Škocjan: Which One to Choose?
| Criteria | Postojna | Škocjan |
|---|---|---|
| Character | The star — spectacular and family-friendly | The secret — wild and raw, UNESCO-listed |
| Visit | Underground train then a 1.5-hour guided walk | On foot only, more steps |
| Don't miss | The olm (“baby dragon”), the concert hall | The Martel Chamber (146 m), the Cerkvenik bridge over the Reka |
| Adult price | €30 (€18 child) | €20 |
| Best for | Families, children under 8 | Nature lovers, hikers |
If you have time, see both — they are 40 minutes apart. Postojna is more family-friendly and more visually spectacular, with the train and the olm. Škocjan is more adventurous, rawer, more moving. For children under 8, Postojna is the better fit. For nature lovers and hikers, Škocjan wins. Either way, bring a jumper: it is a constant 10-12°C underground.
The Lesser-Known Caves
To get off the beaten track: Križna jama cave offers boat tours on emerald underground lakes (booking required, small groups, €20). Vilenica cave, the oldest show cave in the world (open since 1633), hosts an international literary prize every year in its underground ballroom. And Pekel cave (“hell”) near Šempeter is less known but fascinating, with its underground river and waterfalls.
Patrick Faust
French expat in Slovenia since 2004. Founder of e-Slovénie.