A fairytale landscape of looming stalactites, cathedral-shaped rock formations and endless tunnels awaits visitors to Postojnska Jama, the largest cave system in Slovenia. Formed millions of years ago by the Pivka River, the caves span 20km, a quarter of which is open to public tours on foot and by miniature train.

Visitors are offered green felt cloaks to shield them from humidity before the train chugs past underground lakes and enormous caves, including the massive Concert Hall. Many of the stalagmites have assumed strange, humanoid shapes over time, giving the cave network the appearance of a goblin kingdom.

A trip to the caves sometimes allows a peek at the olm, or "human fish". These blind amphibians take their nickname from their human coloring and can grow up to 16 inches long. If you are allowed access to the tanks, be kind and spare these sensitive beasts any flash photography.