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

The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

An underground city of salt.

An institution dedicated to curiosity, logic, riddles, and Mongolia's long history of puzzles.

A huge communist-era propaganda monument and mural that offers stunning views of the Mongolian capital.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

Synagogue built from the stones of Solomon's temple contains the golem of Prague.

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

This tipsy office building in downtown Prague was originally called “Fred and Ginger.”

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

The curious underground history of keeping Paris clean.

A museum dedicated to a secret military hospital hidden beneath a castle in Budapest.

Uh, pardon me, ma'am, but I couldn't help noticing that there's a Columbo statue in the middle of Budapest.

Budapest's Communist-era statues, banished to the suburbs.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

The world's first ice hotel is still one of the most elaborate and beautiful.

The former Nazi concentration camp stands as a museum to remember this dark chapter in European history.

This sprawling concrete suburb of Kraków was designed by the Soviet Union as the model proletarian city.

The silly symbol for an underground protest group is now scattered around the city.

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

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

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

Over time, this castle grew to encompass the entire island.