This elaborately decorated, fairytale-like Romanian royal palace is one of the most striking castles in Europe.

This Ukranian fortress is one of the best-preserved medieval castles in Europe.

The powerful party began with a secret meeting in this shikumen in 1921.

The capital of Cambodia is named after the hill on which this ancient temple complex stands.

Buenos Aires' city of the dead contains some very famous remains, including Eva Perón.

A replica of a 7th-century church hides in plain sight in the middle of the concrete jungle.

An ancient instrument used to measure the waters of the Nile so Egyptian farmers would know whether to expect famine or flood.

This French colonial post office is arguably the grandest in all of Southeast Asia.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

Home to more than 13,000 pieces of war memorabilia and military equipment.

Secret North Korean passage discovered below the world's most dangerous border.

South Korea's largely symbolic, barely used gateway to the North.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

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

Mountain where Jesus was first tempted by the Devil.

The only quarter of the Old City not dedicated to a major world religion.

This newly renovated Soviet-era outdoor exhibition center is bigger than the principality of Monaco.

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

Gliwice Radio Tower, likely the tallest wooden structure in the world.

While the U.S. and Soviet Union were engaged in a space race, Poland built a UFO on the ground.

Originally a leper colony, the island is now an Armenian monastery that's home to an incredible manuscript library and eclectic museum.

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

This hulking behemoth is actually five interconnected towers built in the 1960s.

Twice a day a speeding train passes only inches from the homes of this residential neighborhood.