An abandoned quarry hides an open-air gallery of huge sculptures, some made from the rubble of 9/11.

People have been living in the cave houses on this Italian hillside since the Neolithic era.

Skulls and skeletons are omnipresent in this church dedicated to souls trapped in purgatory.

A fairytale-like medieval church perched atop a rocky cliff on Italy's "Coast of the Gods."

Italian cave with exceptional acoustics and an unsavory history.

Built on a medieval synagogue, this church has a burial crypt, tunnel system, and Jewish ritual bath hiding deep underneath.

According to Greek mythology, this natural spring is the home of a freshwater nymph.

142 ceramic steps become a mosaic once a year.

"Stairs of the Turks", a chalky white cliff eroded conveniently into stairs, allowing for easy pillaging.

This enormous storm barrier is one of the largest moving structures on Earth, with each arm taller than the Washington Monument.

Now a museum, this building was once a 14th-century monastery and the place where the founder of the Dutch nation lived and was assassinated.

The grave of the famous painter is marked by a simple stone in the ground.

A nuclear reactor created for Eisenhower's "Atoms for Peace" campaign is now used for research at a Dutch university.

Pull up and have a drink at a museum filled with hundreds of years' worth of shipwreck artifacts.

A storm shelter built for survivors of shipwrecks.

An awe-inspiring giant blue whale jaw bone stands in the center of this Dutch island.

This beautifully designed star-shaped fort was the premier defense system of the late 1500s.

Now harmless, this looming post struck fear into the heart of medieval troublemakers.

A musical instrument played by the sea.

Construction of this bridge was once described as an "act of violence" against a neighboring country.

A tribute to an iconic act of defiance from the Croatian War of Independence involving a small car.

Trimmed trees grow alongside the graves like topiary tombstones.

Where the lovelorn find a home for their sentimental keepsakes.

This 135-year-old weather station studied the effects of the climate on human health.