Longest road tunnel in the world features an air treatment plant and the illusion of daylight.

A spiralling hourglass-shaped tower rises from the forests in Denmark.

Traditional Danish spot where the schnapps are flowing and the smørrebrød is loaded.

An unconventional and naturalistic sculpture depicting the artist marking his territory on an exterior faculty wall.

Long before ultrasounds and modern testing, medical specimens like these conjoined twins helped physicians learn about congenital anomalies.

The castle used by the Danish Royal Family as a hunting retreat.

The final resting place of the father of modern biological taxonomy.

Dedicated to the European Sinti and Roma peoples murdered during the Holocaust.

A memorial in the Tiergarten is a reminder of the suffering inflicted on homosexuals by the Nazi regime.

Berlin's old airport.

The site where a plot to assassinate Hitler was planned—and its conspirators were executed—is now a powerful memorial to the German resistance during World War II.

After a nearly successful attempt on Hitler's life, the conspirators met their fate in the courtyard of this Berlin building.

This platform is now a memorial dedicated to those who were deported during the Holocaust.

The fairy tale castle of the "fairy-tale king."

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

Stalinist skyscraper built with help of cryotechnology.

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

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

An abandoned set from the 1980 film "Popeye," claimed and repurposed as a theme park by creative locals.

The medieval center of the Islamic world was also once the seat of Saladin's sultanate.

Considered one of the most haunted places in Europe, this 800-year-old castle was home to noble prisoners.

Single runway interrupted by a busy road that cuts across its middle.

A monumental underground karstic wonderland is also the water source for over a million citizens of Beirut.

This modernist cinema has survived war and reconstruction to become a symbol of Lebanon’s revolutionary spirit.