The gorgeous entrances into the city's underbelly look more like grand halls than subway stops.

This building holds the embalmed remains of the leader of the Bolshevik Revolution.

Several cannonballs of mysterious origins decorate two buildings in Stortoget's main square.

The Swedish flag over this small naval fort signals that the nation is at peace.

A king's bloodstained shirt is among the gruesome collection of artifacts displayed below Stockholm's Royal Palace.

This gem from the industrial age helps visitors and residents alike traverse hilly Stockholm.

This grisly exhibit houses skeletons and weapons from a devastating 14th-century clash.

Stockholm's narrowest alley is barely over two feet wide.

The discovery of an old wall led to the creation of this fascinating museum about the city in the Middle Ages.

It is said that each of the white stones in the red facade of this medieval house represents the head of a murdered Swedish noble.

Dine on food tied to Viking history and legend at this subterranean Stockholm spot.

Now a hotel, this former bank was the site of a robbery that spawned a psychological phenomenon.

Sweden's "good old days" painstakingly re-created in a model village.

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

The library's graceful rotunda is like a bibliophile's temple.

It houses the remains of a 17th-century version of the Titanic.

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

Come face to face with the ferocious visage of the serpent-headed mother goddess of the Aztecs.

The turquoise-studded skull of a long-dead Aztec man sits within Mexico City’s Museum of Anthropology.

Once home to an aristocratic family and a workers' organization, this intricately tiled building now houses a chain restaurant.

The most complete statue of this Aztec god sits a top a throne carved with images of hallucinogenic plants.

This foreboding building was the headquarters of the terrifying Spanish Inquisition in Mexico.

This strange sculpture of a menacing skull surrounded by sun rays was discovered at the foot of the Pyramid of the Sun.

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