A Byzantine-era church hidden in a wooded area below the Acropolis.

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

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

Legend says this sacred tree was a gift from goddess Athena.

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

This small 16th-century church in Athens is almost entirely surrounded by a modern building.

The ruined doorway is a portal to the building's turbulent and torturous past.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

The ruins of an ancient Roman tomb hidden in the basement of a trendy clothing store.

A 2,000-year-old computer demonstrates remarkable engineering and astronomical precision.

This tipsy office building in downtown Prague was originally called “Fred and Ginger.”

The abandoned "Ghost Mansion" was left to decay in the mountains of Northern Italy.

An unusual resting place built into the hill with an amazing view of Lake Como.

A 1,000-year-old church holds the bones of the Christian martyrs who died hiding inside it.

An eccentric artist's abode in this small Italian town has been transformed into a surreal temple of mosaic madness.

This trail was once used to smuggle cigarettes, sugar, and other black market goods between Italy and Switzerland.

This crack in France's seaside cliffs once hid a sinister secret.

The sunken structure looks like the victim of a catastrophic flood.

Old vessels have been transformed into artistic canvases in this unusual cemetery.

A massive, secret marina for the Nazis' most formidable weapon in the Atlantic.

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

Local lore says the devil built this beautiful medieval bridge to help a fleeing bandit.

A submerged village appears when dam levels drop.

The camera-toting gargoyle juts out from the exterior of a Gothic cathedral.