Lonely Planet review
The Postojna Cave system, a series of caverns, halls and passages some 20.6km long and two million years old, was hollowed out by the Pivka River, which enters a subterranean tunnel near the cave’s entrance. The river continues its deep passage underground, carving out several series of caves, and emerges again as the Unica River.
Visitors get to see about 5.7km of the cave on 1½-hour tours; some 4km of this is covered by an electric train, which takes you to the Big Mountain (Velika Gora) cavern, on a trip that's like entering the secret lair of a James Bond villain. From here a guide escorts you through halls, galleries and caverns in one of four languages (audio guides are available in a further dozen).
These are dry galleries, decorated with a vast array of white stalactites shaped like needles, enormous icicles and even fragile spaghetti. The stalagmites take familiar shapes – pears, cauliflower and sand castles – but there are also bizarre columns, pillars and translucent curtains that look like rashers of bacon.
From the Velika Gora cavern you continue across the Russian Bridge , built by prisoners of war in 1916, through the 500m-long Beautiful Caves (Lepe Jame) that are filled with wonderful ribbon-shaped stalactites and stalagmites two million years old (it takes 30 years to produce 1mm of stalactite). The halls of the Beautiful Caves are the farthest point you’ll reach; from here a tunnel stretches to the Black Cave (Črna Jama) and Pivka Cave.
The tour continues south through the Winter Hall (Zimska Dvorana), past the Diamond Stalagmite and the Pillar Column, which have become symbols of the cave. You then enter the Conference Hall (Kongresna Dvorana), which is the largest in the cave system and can accommodate 10,000 people for musical performances. In the week between Christmas and New Year, the Live Christmas Crib (Jaslice) – the Nativity performed by miming actors – also takes place in the cave. Visitors reboard the train by the Conference Hall and return to the entrance.
Postojna Cave has a constant temperature of 8°C to 10°C with a humidity of 95%, so a waterproof jacket and decent shoes are essential. Green felt capes can be hired at the entrance for around €2.50. Check the website for package deals, including combination tickets that include Proteus Vivarium and Predjama Castle.