2 Best Sights in Slovenia

The 11 interconnected chambers that compose the Škocjan Jama stretch for almost 6 km (about 4 miles) through a dramatic subterranean landscape so unique that UNESCO has named them a World Heritage site. The 90-minute walking tour of the two chilly main chambers—the Silent Cave and the Murmuring Cave—is otherworldly as winds swirl around the dripstone sculptures, massive sinkholes, and stalactites and stalagmites that resemble the horns of a mythical creature. The highlight is Europe's most extensive cave hall: a gorge 479 feet high, 404 feet wide, and 984 feet long, spanned by a narrow bridge lighted with footlights. Far below, the brilliant jade waters of the Reka River rush by on their underground journey. The view is nothing short of mesmerizing.

This is one of the largest networks of caves in the world, with 23 km (14 miles) of underground passageways. A miniature train takes you through the first 7 km (4½ miles) to reveal a succession of well-lighted rock formations. This strange underground world is home to the snake-like "human fish," on view in an aquarium in the Great Hall. Eyeless and colorless because of countless millennia of life in total darkness, these amphibians can live for up to 60 years. Temperatures average 8°C (46°F) year-round, so bring a sweater, even in summer. Tours leave every hour on the hour from May through October, six times a day in April, and three times a day from November to March.