A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

A pedestrian island in the middle of world-famous Times Square emits a strange (and purposeful) humming noise.

One of only two commuter aerial tramways in the United States.

A crumbling hospital from the 1850s on Roosevelt Island.

The feral felines of Roosevelt Island have a small army of allies and an abandoned hospital all to themselves.

A miniature rainforest is growing inside of a Midtown Manhattan office building.

A centuries-old forgotten underworld lies beneath Malta.

This unique building in the main square stands out among the city's typically Baroque architecture.

This 50-foot-deep sinkhole created in the 14th century is home to rare plants and fungi.

This prison on the Maltese island of Gozo is almost 500 years old, and they have the graffiti to prove it.

This subterranean necropolis holds three floors of antler-dug grave caves.

Burial grounds for more than 1,000 bodies deep under the modern town of Rabat.

An abandoned set from the 1980 film "Popeye," claimed and repurposed as a theme park by creative locals.

The patron of this extravagant Art Nouveau confection insisted that nothing less than a boat should project from its facade.

Rare wooden escalators lead deep down into an otherwise staggeringly monotonous tiled tunnel.

A fantastical 13th-century fortification sandwiched by a modern hotel in central Brussels.

This modern arts center is built around a gem of late-Baroque architecture.

The compass on its front was a handy tool for 17th-century merchants who needed to know the direction of the wind.

Three floors of musical instruments coming from all corners of the world and hundreds of years of musical history.

Tintin's creator is celebrated in an immersive museum that's an astounding work of modern art.

Most prolific publishing house in the 1600s open to the public.

This narrow Ghent alleyway is an officially sanctioned street art tunnel.

This fairytale castle was built as a show of power but was nearly torn down thanks to its history of torture.

This collection of over 50 murals celebrates Brussels' rich history as the self-proclaimed home of the "comic strip."