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

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

This giant urban staircase was built to keep the city's brave fighting men from getting waylaid in the red light district.

A concrete Picasso in the middle of a student housing complex on the outskirts of Stockholm.

Sound travels strangely in this underground whispering gallery.

This giant subway sculpture celebrates the fruit that inspired the theory of gravity.

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

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.

"Only the dead get off at Kymlinge."

Stockholm's tiniest statue is of a small boy looking at the Moon.

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.

Street artists transformed this abandoned industrial neighborhood into one of Europe's largest graffiti exhibitions.

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

A tree that grows parallel to the ground was declared Brooklyn's "crowning curio" by the poet who saved it.

The haunting, dilapidated remains of a former poorhouse on Staten Island's Greenbelt.

A towering spire in the fortress of Kalemegdan honors the victorious armies of Serbia during their struggles against the Ottoman Empire.

Abstract monuments express sorrow and resilience at the site of a horrific massacre in Nazi-occupied Serbia.

A pair of connected skyscrapers form this symbolic gateway.

Destroyed Serbian army headquarters sits half crumbled in a largely revitalized Belgrade.

A Serbian church lit by chandeliers made of weapons.

Structure built from the skulls of vanquished foes.

Hidden in plain sight on the Hudson River is an abandoned train station where nature has taken over.

On the Hudson resides one of the largest clocks in the world.