The ruins of an abbey believed to have been founded by Charlemagne in the 9th century.

This park on the outskirts of Rome boasts two ancient Roman aqueducts and a medieval tower.

A huge enchanting public park just outside the ancient walls of Rome.

France's most famous cemetery, with some of its most curious tombs.

A once-secret library of Freemason history in Catalonia.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

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

The pockmarks across the building's facade are remnants of the Blitz.

Legend says these colorful, invasive residents are the descendants of birds released by Jimi Hendrix.

The sculpture of the deceased cockatoo flops atop its personal plinth.

On October 17, 1814, a 15-ft. wave of beer ran rampant through the streets of London.

There's an exclusive Beefeaters pub hidden in the Tower of London.

A Roman spa buried deep beneath the City of London.

A musical composition 1000 years in length plays at the Trinity Buoy Wharf in London.

This museum tucked below a charming cafe gives a brief snapshot of photographic history.

A little slice of Japan and its aesthetics in London's Holland Park.

Mary Kelly was last seen here before she was murdered by Jack the Ripper.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

This 1920s Dutch barge is now a floating bookstore.

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

A charming 17th-century alley is lined with secondhand bookstores and antiquarian shops.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

This South London cemetery holds the remains of more than 15,000 people.

One of the few remaining casualties of the London Blitz, this destroyed church has become an enchanting public garden.