Postojna Cave in southwestern Slovenia near the town of Postojna is a vast karst cave system formed over millions of years. Visitors can explore its passages on a guided tour, travel part of the route by underground train, and observe distinctive rock formations and cave-dwelling species in a managed environment. It is notable for its extensive network. Within the cave, visitors can see a prominent stalactite formation often described as diamond-like and observe the so‑called “dragon babies.”