A top secret Cold War bunker hidden beneath a Latvian spa facility is now open for tours.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

On a site with a long military history, a 1980s shelter.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

A taste of the macabre Tokyo's ritzy shopping district.

Six beautiful wooden giants are hidden around Copenhagen.

An artist has turned what most people would consider a bathroom nightmare into a work of political art.

Visitors are treated to a stained glass kaleidoscope interior inside this work of art.

The world's first combination ski slope and power plant.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

Beneath Denmark's Højbro bridge, a bronze merman and his seven sons forever mourn for the mother and wife who left them for land.

A little-known cafe in an old copper bridge tower with 360-degree views of the harbor.

Danish tourist destination well known for open stalls where vendors sell marijuana on the street.

Hans Christian Andersen for the postmodern world.

An enormous, inside-out glass globe built in 1935.

America's oldest archaeological site or a muddled case of wishful thinking.

In 1958, an MIT fraternity pledge laid down on this bridge and instituted a new, unique unit of measurement.

Painstakingly built dioramas sit unnoticed in a Boston office building.

The former locus of Boston's high culture has been shuttered and buried for over 70 years.

This upscale streetwear store is hidden behind a fake Snapple machine in the back of a deli.

A network of concealed passageways lies within a busy London Underground station.

Beating out all other concrete competitors, this massive garden feature's pointy hat has earned it a world record.

The curios of pharmacist and collector Henry Wellcome.

Never actually a tree at all, this spot was the site of London's public hangings for nearly 600 years.