A black cat protests the City Guild in Riga's Old Town.

Flamboyant architecture from the turn of 20th century.

The oldest housing complex in Riga is a mini timeline of architectural trends.

3,000 market stands in five former Zeppelin hangars.

An alien church provides much needed silence in the midst of a Finland shopping center.

A subterranean house of worship carved right out of the bedrock.

Architecturally stunning library serves as the hub of Finnish scholarly life and culture.

Stockholm's deepest subway station is also a stunning ecological wonder.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

Home to three historic ships from the age of Vikings.

Walk 2,300 feet above the ground on the "Troll's Tongue."

Pre-Nazi swastikas adorn the sculpted pachyderms flanking this brewhouse portal.

The de facto symbol of Copenhagen is this bronze fairytale which cannot seem to keep its head for very long.

This sublime architectural marvel is a rare example of an expressionist church.

Started as a kitchen garden, now the second largest botanical garden in the world.

This futuristic German spa allows visitors to float in a pool of salt water while zoning out to underwater techno.

Museum preserving torture methods from the past.

The world's only museum devoted to the wonders of fluorescence.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the first ‘Harry Potter’ film.

The fountain marks the area where hundreds of accused witches were burned at the stake.

This 17th-century street hidden beneath Edinburgh was once a breeding ground for the black death.

Frida Kahlo's childhood home, now a museum of her life and works.