Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

Large collection from the 3rd millennium BCE.

This ancient hydrological marvel is now the base of a modern outdoor cinema.

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

This now abandoned restaurant provides some of the most amazing views of Lisboa.

This demon atop the Notre-Dame de Paris looks utterly bored.

Inside a former cabaret, seven floors of erotic art.

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

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

The industrial architecture honors the laborers who brought the Exposition Universelle of 1900 to life.

The macabre collection of Jacques Sirgent, an expert scholar on the undead and all of their trappings.

An ancient octagonal weather station named for the eight Greek gods of wind.

This innocuous-seeming building is actually the remnant of a major wartime brothel.

The floorboard scrawling of a tragic madman is on public display outside a Paris hospital, much to the dismay of its opponents.

135 bronze medallions mark a French meridian line which once rivaled the hotshot Greenwich timeline.

19th century pendulum and a clock restored by a rogue group of guerilla artists.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

A 16th century chapel decorated with bones, skulls, and entire bodies hanging from the wall.

Skulls from the plague of 1656 and World War II bombings are united by a cult dedicated to caring for the ancient dead.

This magical-looking island is notorious for the misfortunes suffered by its owners.

The Neapolitan Cult of the Dead still cares for the skulls at this mini-Fontanelle.

A former steam-powered mill from the 1800s is now an industrial park with a giant steel dragon slide.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.