A science fiction-inspired apartment building designed by a famous Spanish architect.

A Romanesque tower appears when water levels drop.

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

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Step inside the first house designed by Catalan architect Antoni Gaudí, considered to be one of the first Art Nouveau buildings.

A steel paper plane is all that remains of a crashed aircraft that caused an amazingly small amount of damage.

This declassified Cold War bunker hosts a large collection of Swedish aircraft.

Despite the groans of archaeologists, this astounding groups of Bronze Age petroglyphs have been painted red for tourists.

An early 20th-century bullring converted into a modern shopping center.

Catalonia Tradition: Beating the hollow Christmas log until it defecates in your fireplace.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

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

A Japanese video game arcade hides in the back of a Swedish pool hall.

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.

The remains of Alfred Nobel's first nitroglycerine factory can still be found on the shores of a Swedish bay.

This Stockholm light tower can be controlled by anyone with a smartphone.

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

Mountain where Jesus was first tempted by the Devil.

Hidden in plain sight, Sweden's official ordnance datum is now abandoned.

A wooden street sign is the last remnant of this 400-year-old alleyway.

A golden plaque marks the site of the mysterious unsolved assassination of the former Swedish prime minister.

Sweden's oldest animated sign is still lighting up the skyline today.

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.