Postojna Cave is a 24-kilometre karst system carved into the Slovenian limestone — the longest cave system in the country and the most visited show cave on the continent. Visitors have been touring its galleries since 1819, just one year after its main passages were discovered. The standard 90-minute tour covers 5 kilometres: 3.7 km on an electric cave train (running on tracks since 1872 — the world's first underground tourist railway) and the rest on foot through five enormous halls.
Highlights along the route include the Spaghetti Hall with thousands of needle-thin stalactites, the Brilliant — a 5-metre-tall white stalagmite that's the cave's mascot — and the Concert Hall, a 3,000-capacity space with the best acoustics underground in Europe (used for concerts every August). The cave maintains a year-round temperature of 8–10°C and 95% humidity, so a jacket is essential even in summer. Most striking biologically is the olm (Proteus anguinus), a blind, pink-skinned cave salamander that can live a century, displayed live in a small viewing tank near the end of the tour.
Postojna pairs naturally with Predjama Castle 9 km away — a single combination ticket (around €43) covers both and is what most visitors do. Allow a full day: morning at Postojna (the cave tour), lunch in town, afternoon at Predjama. Dragon-themed merchandise everywhere references the legend that olms were thought to be baby dragons washed out of caves during floods. From Ljubljana, Postojna is 50 km southwest — under an hour by car, 80 minutes by hourly bus.
