These warring psychedelic crags commemorate an unsuccessful military operation.

Outside of one of Britain's most renowned social clubs, a step installed specifically for the Duke.

This railroad track was so secretive that it was omitted from all maps.

Once the "Eighth Wonder of the World," this iron railroad bridge was decimated by a tornado.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

A dark, narrow tunnel that leads to a charming lake and waterfall.

This post-war motel embodies a little-known, Miami-born architectural style.

The tunnel's elegant proportions keep you snug with no claustrophobia freak-out.

In Hong Kong, a fairytale flower tunnel is hidden within the gardens of a public housing complex.

Hamburgers are intensely proud of their tunnel beneath the river.

The romantic botanic tunnel feels like a well-kept secret.

A repurposed railway tunnel with otherworldly acoustic characteristics.

The U.K.'s first underground railway line is now a lively thoroughfare for runners and cyclists.

This former train tunnel is filled with lines from a poem crafted by Robert Louis Stevenson.

This brick-lined pedestrian walkway was once a railway tunnel used during the Civil War.

Home to the longest wooden escalators in the world.

Once a sewer culvert, this road tunnel now offers cyclists and pedestrians a subterranean stroll under the C&O Canal.

An abandoned railroad tunnel transformed into a creepy path for hikers and cyclists.

This nondescript tunnel has been featured in a number of iconic movies, from “Roger Rabbit” to “Back to the Future.”

This Connecticut ferry has been operating in some form since 1655.

During World War II, Austria's oldest salt mine was used to store thousands of pieces of stolen artwork.

A nearly 500-year-old sculpture depicts a man eating a sack of babies, and no one is sure why.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

Residents of Berlin take their coffee and cake in one of the city’s most restful spaces: a cemetery.