This ancient theater was once the home of fierce gladiatorial battles.

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

This stunning French estate was so lavish that it landed its original owner in jail for the rest of his life.

Massive puppet-automaton machines created by French artist collective Machines de l’Ile.

The famous winding walk at Chartres is surrounded in mystery and myth.

This massive blockhead sculpture hides an entire library.

A Gothic cathedral created from volcanic rocks.

A haunting collection of the vanished and disappearing natural world.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

These wire animal sculptures commemorate the exotic inhabitants that once called the Tower of London home.

A quiet memorial to those who died saving others in the heart of the City of London.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

Lovers proclaim their unbreakable bond by leaving their names on locks fastened onto the Shoreditch fence in East London.

Richard III supposedly disposed of his nephews' bodies here in an effort to seal his claim to the throne.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

This hidden green space is the city's second largest conservatory.

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

During the summer months, giant teddy bears take over Paris near Les Gobelins metro station.

The video game-themed street art first popped up in the French city.

The tradition of open-air secondhand and antiquarian bookselling in Paris dates back to the Renaissance.

Once a 19th-century brasserie, this McDonald's exterior celebrates Alsatian design and the "King of Beer."

This structure atop a craggy cliff in one of the most beautiful parks in Paris boasts an unbeatable view.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

A Parisian exterminator's shop whose storefront displays stuffed rats hanging from traps.