Medicinal spa created with the discharge from a geothermal energy plant.

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

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

A monument to the thousands of Canadian soldiers who died capturing the French ridge during World War I.

A Dutch clog company in the town of Zaandam loves the wooden shoes so much it made a museum for them.

Some 80,000 Delft Blue tiles line the inside of this Amsterdam walkway.

Pilgrimage site for star-crossed lovers.

Vienna's diversity-themed traffic lights were inspired by the Eurovision Song Contest.

Baroque celebration of the end of the Great Plague of Vienna.

Museum devoted to the artificial language of Esperanto.

Handsomely crafted representations of our round planet.

In the middle of a Vienna square, Roman ruins dating back some 2,000 years are on display.

Built to give thanks for the passing of a plague epidemic, this cathedral is a one-of-a-kind architectural hybrid.

Despite attempts by local police to discourage it, Beatles-inspired graffiti has been a means for artists to air grievances for decades.

The palace window through which Protestant nobles flung two Catholic regents, thus sparking the Thirty Years' War.

Countless grotesque faces stare out from this eerie Prague art wall.

Two stunning 17th-century libraries and a cabinet of curiosities.

This automated sculpture of two men peeing will spell out text messages with their micturition.

This walkway is so narrow it needs its own light to stop pedestrian traffic jams.

A Jenga-style cylindrical tower of books that appears to go on forever.

The oldest arboretum on the Dalmatian coast doubles as the gardens of Kings Landing in "Game of Thrones."

Where the lovelorn find a home for their sentimental keepsakes.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

The holes in this wall provide a glimpse into Jewish life in Budapest, both past and present.