Postojna Cave is one of the world’s great show caves, an immense karst system a short trip from Ljubljana. Ticketed visitors board a little electric train that trundles deep into the mountain before continuing on foot past soaring chambers, forests of stalactites and the ghostly baby dragons, the olms, that live in its waters. Vast, dramatic and easily accessible, it is one of Slovenia’s most popular attractions and often combined with the nearby clifftop Predjama Castle.