Postojna Cave

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 runs as far as the Big Mountain (Velika Gora) cavern. Here you stand under one of the five signs identifying your language, and a guide escorts you through halls, galleries and caverns.

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 furthest 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 Concert Hall (Koncertna 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 actors - also takes place in the cave.

The bizarre pink creatures you'll see in a tank at the end of the tour are Proteus anguinus, unique 'human fish' first described by Janez Vajkard Valvasor.

Postojna Cave has a constant temperature of between 8°C and 10°C with a humidity of 95%, so a waterproof jacket is essential. Green felt cloaks can be hired at the entrance. Check the website for package deals including combination tickets. The two hundred species of fauna (including cave beetles, bats, hedgehogs, and the 'human fish') found in the cave are studied at Proteus Vivarium (research station located in the cave).