At this 16th-century monastery in rural Bulgaria, visitors can also spend the night.

A flamboyant five-story building in Bulgaria resembles a crawling snail.

This scale model of our solar system hid in plain sight for years before a physics team sought out all the planets.

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

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

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

Massive puppet-automaton machines created by French artist collective Machines de l’Ile.

This Parisian fountain is a little bit fantasy and a little bit nightclub.

A series of abstract, silly sculptures represent the works of a great modern classical composer.

This modest marker near Notre Dame identifies the very center of Paris.

Abandoned railway line circling the city of Paris.

Ghosts of France's colonial past.

Arguably Belgrade's only example of pure Art Deco architecture.

Destroyed Serbian army headquarters sits half crumbled in a largely revitalized Belgrade.

A subterranean house of worship carved right out of the bedrock.

Dedicated to the outnumbered Finnish forces who pushed back Soviet forces during the conflict.

These enormous, stern-faced statues greet visitors with lanterns, and sometimes costumes.

An abstract monument to a symphonic composer.

Home to nearly a third of the world's mud volcanoes, Azerbaijan is home to a messy, bubbling, and sometimes explosive landscape.

A shrine of fire worship built on top of a natural flame.

This mysterious but iconic tapered tower appears in many Azeri fairytales and legends.

The building's fluid, wavelike walls are a true feat of architectural ingenuity.

Mysterious hillside with a continuously burning natural fire.

An ancient knight and a symbol of the city's freedom.