One of the world’s largest living advertisements is made out of pine trees.

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

A hidden bathhouse in one of Stockholm's oldest and busiest neighborhoods is open to anyone who can find it.

A series of modernist treehouse hotel rooms grace the outskirts of an Arctic forest.

Sweden's first nuclear reactor, R1, can be visited 25 meters underground.

An illuminated manuscript comprising the life's work of a lone monk, inexplicably decorated with a portrait of Satan himself.

150 or so scrounged-up lamps, chandeliers, and lanterns light up this alley in central Athens.

This small chapel holds the mummified heart of one of the heroes of the Greek Revolution.

A man's head is enshrined beneath a statue near the first building constructed for the modern Olympic Games.

This once architecturally advanced housing complex is now a haven for squatters that still bears the scars of war.

Scars of this building's past life as a violent prison still cover its walls.

A crushed gate and giant bronze head serve as a reminder of Greece's fight for freedom.

A Byzantine-era church hidden in a wooded area below the Acropolis.

There are many Byzantine-era churches still standing in Athens, but this is the only one with a 2,500-year-old column rising through its roof.

The only surviving choragic monument is a trophy awarded in 334 BC for the winning dramatic chorus.

The site where hundreds of Greeks were tortured by the Nazi secret police is now a cosmetics store.

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

A grotesque collection of wax limbs depicting the symptoms of venereal disease.

The ruined doorway is a portal to the building's turbulent and torturous past.

The oldest cemetery of modern-day Athens blends the modern and ancient worlds.

Large collection from the 3rd millennium BCE.

This ancient hydrological marvel is now the base of a modern outdoor cinema.

An ancient octagonal weather station named for the eight Greek gods of wind.

This mystical orb covered in strange symbols is thought to have been used in ancient Greek magical rituals.