This irregularly shaped sea fortress has defended not one but three different sovereign states.

Stockholm's narrowest alley is barely over two feet wide.

A hidden bathhouse in one of Stockholm's oldest and busiest neighborhoods is open to anyone who can find it.

Sweden's "good old days" painstakingly re-created in a model village.

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

This demon atop the Notre-Dame de Paris looks utterly bored.

Claude Monet was baptized in this lavishly ornate Paris church.

What looks like a normal building is really a hollow facade hiding a subway vent.

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

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

The vast, legendary catacombs hold secrets much stranger than stacked bones.

This chimerical bridge/tunnel appears to dead end right into the sea.

A replica of the beloved character's house, modeled after the author's own drawings.

A replica of the home of a famous fictional troll family.

These engineering masterpieces are a dominant feature of the Belfast skyline.

Preserved "bog person" that is over 2,000 years old.

The final home of the legendary Danish sailor said to have lived to be 146 years old.

A symbol for the opposition to nuclear power around the world.

A public display of random paleontology.

This colorful artistic feature atop a Danish art gallery allows visitors to stroll through a rainbow.

This trio of Australian rock spires may have inspired aboriginal legend or just modern tourism.

Come for the flowers, stay for the bats!

Though considered an eyesore by some, this boxy Brutalist high-rise plays a significant role in Sydney's past.

A forest of immensely tall and unusually straight oak trees planted nearly 200 years ago to build naval ships that never came to be.