The 2,000-year-old Roman columns are hidden within Barcelona's Gothic Quarter.

A secret, ethereal waterfall beneath the picturesque gardens.

This mill has been in continuous operation since before the country’s founding.

Decorative folk arts dot the countryside barns of Berks County. 

This unusual rock formation in Berks County is nearly a mile long and may date from the Ice Age.

This 11th-century fortress is now the seat of Aragon’s state legislature.

Europe's largest river aquarium features freshwater species from around the world.

This fantastical faceless sculpture in Spain is on the grandest scale.

The Museum of the Forum of Caesar Augusta showcases the city's ancient Roman sewage system.

The mansion home of author Edith Wharton.

An emerald-green grotto just a short trip from Austin.

One of the world's tallest Ferris wheels takes visitors high above Las Vegas in a spinning party room.

The park is home to the United States's only still-operating Dutch windmill.

This surreal statue brings a famous French novel about a supernatural cad to arresting life.

Montmartre's sole surviving windmill became an iconic landmark for 19th-century painters, artists, and bohemians.

A museum dedicated to one of Paris’s most famous residents, tucked into a corner of one of the city’s most famous squares.

An overlooked marble is the only surviving in-place 18th century example of the measurement that changed how we define distance.

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

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

The U.S. Navy's last diesel-electric submarine rests half-submerged in the middle of Portland.

This huge, disused viaduct is now a crumbling concrete underworld of covered in years of graffiti.

The remains of a community that was forced to move for a dam that never materialized still rot in this Pennsylvania park.

Twenty-three trees, each paired with a basalt stone, line a street in Chelsea, continuing an urban project started by German Fluxus artist Joseph Beuys.

Commemorating the spot where the famous scientist fed his pigeons.