This massive library holds what was once the largest book collection in the world.

So opulent and massive it was once dubbed a palace, this hotel's doors closed temporarily in 2007 and failed to reopen.

This abandoned building, which is the second-largest structure on the Maltese island of Comino, has a complicated past.

Burial grounds for more than 1,000 bodies deep under the modern town of Rabat.

This unique building in the main square stands out among the city's typically Baroque architecture.

Valletta’s outdoor theatre stands within the ruins of a 19th-century opera house.

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 underground tropical garden sits inside a Paris Métro Station.

A quarry cum sculpture park where the works of art are chiseled into the very walls.

The vibrant buildings in the “capital of the comic strip” celebrate the art form that made it famous.

A tiny, forgotten park of surrealist sculptures in Angouleme.

Home to the oldest operating roller coaster in the Southern Hemisphere.

Cooled, fractured lava formed this geometric rock feature.

This monumental work of art symbolizes the coming together of a previously divided city.

A sublime medieval path adorns the marble floor of one of the most beautiful Gothic cathedrals in France.

This massive redwood tree has a hole in the base big enough to drive through.

One of the most scenic stretches of road in America winds between some of the country's oldest trees.

Staircase winds down the side of Telegraph Hill through gardens, wild parrots flying overhead.

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

The location of this small park was once the site of an infamous public morgue.

Site of a classic 19th-century physics experiment to prove the earth is rotating.

The remaining relics of the patroness of Paris lie in a chapel under a striking double spiral staircase.

A island reachable by a causeway at low tide is possibly one of the earliest Western European locations to be identified in text.

An opulent monument built for a duke who donated his entire fortune to the city of Geneva.