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

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

France's most famous cemetery, with some of its most curious tombs.

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

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

Theme park featuring miniature replicas of European monuments.

A little sculpture with a large wardrobe.

Climb inside an iron crystal magnified 165 billion times its normal size.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

The spot where the fascist dictator made some of his most famous speeches including declaring war on Britain and France.

2300-year-old Roman road connecting the empire.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

The yawning maw of this pagan visage is said to bite off the hands of liars.

The only museum with its curator—and her pets—buried inside.

Two stone columns flank the grand Venice square, but there were supposed to be three.

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

Go inside to really appreciate this 500-year-old technological masterpiece.

This community on a small Venetian island has taken to painting their houses in bright neon hues.

Gilded heaven for philatelists and architecture freaks, still in full working order despite sitting atop tremulous ground.

The famous artist couple lived and worked here, in two different houses separated by a bridge.

This rare volcano spews the strangest and (literally) coolest lava in the world.