Snowbird's Peruvian Tunnel

Every winter, the wind carves blocks of frozen water into beautiful abstract shapes inside this unusually curved tunnel.

The remains of an abandoned funicular railway that once ferried skiers and hikers to great heights in the Pyrenees.

Nature has shaped this drainage tunnel into the digestive tract of a mighty beast.

A network of ancient tunnels and vaulted chambers with mystical Buddhist reliefs, built for ascetic training.

Stuck in a bygone era, the oldest subterranean shopping street in Japan hides beneath the popular Asakusa district of Tokyo.

The largest underground pedestrian tunnel system in the U.S. mostly caters to the people working in the offices above, but provides a great, air-conditioned way to traverse the city.

This 300-foot-long underground tunnel was once used to transport food from the kitchen into the main building.

Would you spend the night in Japan's deepest train station?