Postojna Caves, Slovenia

Postojna Cave — the Queen of Cave Systems. Stretching more than 24 kilometres beneath the Slovenian Karst, it is one of the largest and most magnificent cave networks in all of Europe, and by far the most famous of Slovenia’s underground wonders.

The scale is breathtaking. Vast halls open one after another, each with its own character and colour, adorned with stalactites and stalagmites hundreds of thousands of years in the making — some of the formations you pass are up to half a million years old. Its great symbol is the ‘Brilliant’, a five-metre pillar of pure snow-white calcite that gleams as though lit from within. The journey ends in the colossal Concert Hall, a cavern so large it can hold thousands of people and whose extraordinary acoustics have welcomed full symphony orchestras beneath the living rock.

What makes a visit truly unique is how you enter this underworld — aboard a little electric railway. Opened in 1872, this was the world’s first underground cave railway, and it remains the only cave in the world you tour by train. The open carriages carry you some 3.5 kilometres deep into the mountain, winding gently past galleries and formations, before a further 1.5 kilometres is explored on foot with a guide. The air holds steady at around ten degrees all year, and the whole tour takes about an hour and a half.

Postojna is also the most biologically diverse cave on Earth, home to more than a hundred species found nowhere else. Most beloved of all is the olm (Proteus anguinus) — the pale, blind, entirely aquatic ‘human fish’, Europe’s only cave-dwelling vertebrate, which can live beyond a hundred years and survive years without food. For centuries local people, glimpsing these strange creatures washed out by floodwaters, believed them to be baby dragons — the offspring of a great dragon said to dwell in the depths of the cave. They can still be seen today in the cave and in its Vivarium, where in recent years the ‘little dragons’ have even hatched their young.

To ride down into Postojna and stand among its shining halls, listening to water shape the stone drop by patient drop, is to enter a fairytale realm older than memory itself.