A marvel of Byzantine engineering under the streets of Istanbul.

Six times a day a train runs right through the middle of this Thai street market, sending vendors scrambling.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

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

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

Elaborate tile work in this railway station tells the story of Portugal.

This gorgeous space is England's largest independent library outside of London.

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

What started as a tongue-in-cheek shrine is now a full-blown museum celebrating "The Hoff" and his longtime love affair with Berlin.

The site of the famous Nazi book burning campaign of 1933 remembers its "Night of Shame".

The largest free-standing aquarium in the world resides in a hotel lobby in Berlin.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

The oldest Roman lighthouse still in use.

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

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

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.

An accidental trick of light casts the perfect shadow of a pilgrim of the Camino de Santiago against the cathedral wall.

Thanks to an acoustic anomaly, this unassuming stone bench has heard one hundred years of secrets.

Twice a day this ancient path disappears with the tides, leaving the Holy Island of Lindisfarne out to sea.

The nearly 200-year-old folly has a secret spiral staircase hidden in one of its pillars.

St. Mary's Asylum was isolated and abandoned before being converted into a Bed and Breakfast.

Natural stone arches form a walkable "cathedral" at low tide, then disappear entirely when the water returns.

Remarkably intact Roman stone fortifications have encircled this Spanish city for centuries.