Twelve grave-faced marble angels guard the emperor's tomb at Les Invalides.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

This bridge was constructed from the rubble of the infamous Bastille.

This life-size replica of the Statue of Liberty's flame is also a tribute to Princess Diana by default.

A surrealist timepiece by the artist of melting clocks.

Paris' linguistic guide to the international language of, yes, love.

The very center of Paris is surrounded by a bevy of strange good luck rituals.

A collection of old neon signs from all over Poland line a secluded courtyard.

Hundreds of caves once used to store grains and animal feed.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

What was once an underground Nazi city is now Europe's largest bat reserve.

This Swedish astronomical clock was in storage for almost a century before its glorious workings were put on display once more.

Come to this Polish museum to take a good, clean look at filth.

This symbol of Polish heritage survived the occupation during World War II, hidden in plain sight.

An abandoned Nazi explosives plant founded by the inventor of dynamite is now an underground museum.

Stockholm's deepest subway station is also a stunning ecological wonder.

A mysterious structure left behind on the Polish mountainside, sometimes called "Hitler's Stonehenge".

The celebrated eyesore created by starry-eyed sweethearts.

The ruins of a 13th-century monastery that long served as a place of refuge from wars and raids.

Climb around the high waterfalls on series of iron ladders and bridges within the wildest gorge in the Slovak Paradise.

The 700-year-old fortress was the site of Count Orlok's castle in "Nosferatu."

It houses the remains of a 17th-century version of the Titanic.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

This Belgian theme park began as a refuge for bored church children and was closed down when a boy lost an arm.