Once the world's largest reinforced concrete structure, this abandoned bridge now beckons urban explorers.

World War II bunker still standing on the New Jersey beach.

Lumps of significant stone from around the world surround a flaming monument for peace.

This elaborate High Victorian Gothic structure is one of the world's few 16-sided buildings.

Five candy-colored villages on the Italian Riviera.

This amazing medieval fortress stands atop a promontory along the famous Cinque Terre.

The bomb-ravaged remains of of a colossal Neptune.

This massive blockhead sculpture hides an entire library.

A tribute to Ponce de Leon's supposed quest for eternal youth.

An underwater city for the dead.

Welcome to old Florida, where a 1940s mermaid show is still enchanting visitors.

A man-made island in scenic San Francisco Bay.

Florida's oldest bar was once a morgue, complete with a hanging tree and gravestones.

A historic presidential getaway on the continental United States' southernmost island.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world’s largest coastal brick fortresses.

This anatomical sculpture raises awareness about violence against women and promotes gender equality.

Original cabaret handbills, posters, and feline artwork are a purrfect highlight of the Museum of Montmartre.

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

The tomb of history's greatest potato promoter is surrounded by tubers.

During the summer months, giant teddy bears take over Paris near Les Gobelins metro station.

The approximate spot where the last Grand Master of the Knights Templar was put to death.

The tradition of open-air secondhand and antiquarian bookselling in Paris dates back to the Renaissance.

Once a 19th-century brasserie, this McDonald's exterior celebrates Alsatian design and the "King of Beer."

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.