The ruins of this Dutch castle sit atop a labyrinth of once-secret tunnels and passageways, dating back over 900 years.

Hidden within a Netherlands crater is a stone bed that lets those who lie in it see the sky as a curved surface.

An Amsterdam street lined with antique shops each one dedicated to a different obscure collection.

The fanciest public restroom in New York City boasts fresh flowers, art, and a classical music soundtrack.

Sculpture designed by Turkish artist and professor Mehmet Ali Uysal.

Hiding the longest subterranean river known in the world.

The Devil’s own choice when he needs a drink in Brussels.

Part modern art project, part traditional chapel, this see-through church is only substantial from the right angle.

This is what trains will look like after the zombie apocalypse.

The tiny Belgian town's ancient version of Mardi Gras involves eerie wax masks, sticks for warding off evil, and ostrich plume hats.

The oldest Dutch colonial stone house in New York City is a hidden gem on the border of Brooklyn and Queens.

One of the oldest Jewish cemeteries in the city, it is now overgrown with an urban forest.

Two New York rooftops are home to the largest rooftop soil farms in the world.

Piano-making empire filled with 200-year-old steam machines still churning out 1,000 instruments a year.

A once crucial portion of the Long Island railroad still lays abandoned, waiting to be turned into an urban park.

A hyper-luxurious, 12,000- square foot home might be buried beneath Queens, still waiting to protect you from nuclear missiles.

1800 rooms of single-family residence in Brunei.

These stark white cliffs were spat up by the sea and are slowly being retaken by it.

A centuries-old complex of hand-dug stone chambers has sheltered locals in times of trouble.

Legend has it this 11th-century castle was paid a visit from the devil.

The largest underground church in Europe.

The post-apocalyptic remnants of a bucolic town ruined by a plane crash.

A charming flea market shop dedicated to retrofuturistic apparati.

This Paris art space celebrates the creativity and ingenuity that springs from abject poverty, especially in Africa.