This picturesque medieval monastery guards a small trove of historic treasures.

A wunderkammer of gold and silver reliquaries and ancient saintly bones.

Humble beginnings for one of the world's most famous scientists.

Gargoyle head that brings good luck.

Once a state-of-the-art tuberculosis treatment spa, these ruins are now ruled by paintball players.

The complex has been abandoned since the Croatian War of Independence, barring a stint as a set for 'Game of Thrones.'

Legend has it fairies gathered at the site of this medieval castle.

This truly palatial work of Communist-era architecture now sits crumbling on a Croatian beach.

Yugoslavia's biggest underground airport lies in ruins.

A musical instrument played by the sea.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

An ethereal glowing blue ocean cave in Croatia.

When a supermarket opened up shop within a medieval building it became protected by UNESCO on a technicality.

A sprawling collection of books and manuscripts about ancient Greece that would have put their famed libraries to shame.

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

The oldest cemetery of modern-day Athens blends the modern and ancient worlds.

The railway carts travelers to central Athens's highest peak, which offers stunning vistas of the city.

Stockholm's deepest subway station is also a stunning ecological wonder.

This Stockholm light tower can be controlled by anyone with a smartphone.

The library's graceful rotunda is like a bibliophile's temple.

An illuminated manuscript comprising the life's work of a lone monk, inexplicably decorated with a portrait of Satan himself.

The unexpectedly beloved remnants of a controversial thermal power plant.

One of the most photographed buildings in a city known for its Modernista architecture is an abandoned squat.

Step inside the first house designed by Catalan architect Antoni Gaudí, considered to be one of the first Art Nouveau buildings.