This picturesque Umbrian city has a subterranean side that has long remained hidden.

This seaside Italian village doesn't just look Escher-esque, it actually inspired the mind-bending artist.

An unusual "skull with ears" sits in the crypt of this small church tucked away at the end of a narrow alley.

A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

Monsters and miniatures are held in equal esteem at this wondrous museum.

After being destroyed by IRA sympathizers, the ruins of this stately Irish manor have sat vacant for decades.

Thousands of tourists and residents in Cologne affix "love padlocks" on the Hohenzollernbrücke Bridge to symbolize their affections.

Built by the Ancient Greeks, this chariot bridge is still in use today.

This legendary city has been a tourist attraction for centuries.

The hallucinogenic center of the ancient world.

What once sat in the world’s spotlight is today a largely disused ghost complex.

This gem is often wrongly overshadowed by the larger, newer Metropolis church in Athens.

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

This centuries-old Italian chapel hangs midway down a sheer cliffside.

The bombed out remains of the old church were kept intact next to the new one, as a reminder of the futility of war.

The oldest inn in England served brew to the crusaders.

The haunting concrete remains of a Nazi pebble crusher can still be found in this small French commune.

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

A monument to the three wars that led to German unification towers within a Berlin traffic circle.

After a nearly successful attempt on Hitler's life, the conspirators met their fate in the courtyard of this Berlin building.

Metro station with a claim to rock n' roll fame.