Visiting Postojna Cave

The train. The visit starts with a 3.7 km ride deep into the cave on a small open train. Postojna opened the world's first cave railway in 1872, and it's still the only double-track railway inside a cave. The train rattles through narrow tunnels and past lit chambers before dropping you at the start of the walk. It's about 10 °C inside all year, so bring a warm layer.

The stalactites and stalagmites. On foot, a guide leads you through halls packed with dripstone: stalactites hanging from the roof, stalagmites rising from the floor, and columns where the two have met. It grows painfully slowly, on average about 1 mm every ten years, so the "Skyscraper", a 16 m stalagmite on the route, is dated at around 150,000 years old. You also pass through the Big Mountain, a collapse hall large enough to fit St Paul's Cathedral, and see the Brilliant, a 5 m stalagmite so bright white it has become the cave's symbol.

The olm. Along the way you'll see live olms (Proteus anguinus), the cave's most famous residents. They're pale salamanders, 20–30 cm long, whose eyes are covered by skin, and they can go years without food and live to around 100. In the 17th century, people in Postojna believed a dragon lived in the cave and that olms were its young, which is why they're still called "baby dragons". Locals also call them the "human fish". In 2016 an olm laid eggs in an aquarium inside the cave, and visitors could watch the young hatch, a first for the cave.