Postojna Cave & Predjama Castle day trip from Ljubljana

Postojna Cave – Postojnska jama in Slovenian – is one of the largest show caves in the world, and the only one most visitors reach by train – a 19th-century underground railway that's been carrying people into the karst (the limestone landscape that gave the geological term "karst" its name, from this very region) since 1872. Paired with nearby Predjama Castle (Predjamski grad), built directly into a cliff face, it's Slovenia's most-booked day trip by a wide margin.

A cave with its own railway

The cave system was carved by the Pivka River, with the first documented visitors dating back to the 13th century, though the most spectacular chambers weren't discovered until 1818. The underground train, opened in 1872, was the first railway ever built inside a cave – it carries visitors around 2km into the system before a guided walk continues on foot through halls of stalactites and stalagmites. The cave also holds a rare resident: the olm, a blind, pale-skinned salamander nicknamed the "human fish," capable of living up to a century and surviving years without food.

The castle built into a cliff

A short drive from the cave, Predjama Castle is built directly into the mouth of a cave on a 123-metre rock face – the largest cave castle in the world. Its most famous resident, the 15th-century knight Erazem Predjamski, used the castle's hidden tunnels to smuggle in supplies during a siege by the Habsburg Emperor's forces, holding out for over a year before a servant betrayed his exact location and he was killed by cannon fire.

Getting there

Postojna is about 50km from Ljubljana, under an hour by car – comfortable as a single day trip covering both the cave and the castle.

Booking

A combined tour from Ljubljana covers return transport, skip-the-line entry to both the cave and the castle, and a guide who fills in the history at each stop. It's the most-booked day trip from Ljubljana and can sell out in peak season, so book a few days ahead.