A tiny church on a man-made island in the Adriatic.

A curious cave church carved into the face of a cliff.

A musical instrument played by the sea.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

A Red Cross memorial museum at the site of the Niš concentration camp that operated for four eventful years during World War II.

For over 40 years, this quaint little house has teetered on a rock in the middle of a river.

A pair of connected skyscrapers form this symbolic gateway.

Nikola Tesla's ashes are held in a golden sphere, surrounded by his works.

Structure built from the skulls of vanquished foes.

This fortress dates back to the 6th century and is also the site of a controversial abandoned restoration project.

This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

One of the most controversial statues in Romania is an emperor with no clothes.

This once-derelict building is now one of the most beautiful bookstores in the world.

The ancient Greek Titan guards this massive dam holding a lightning bolt to symbolize electricity.

The legendary cliffside castle of three-time Voivode of Wallachia, Vlad the Impaler.

This massive concrete sculpture is said to be the heaviest communist monument on Earth.

A giant portrait of an ancient king looms over the river.

Romania's triumphal arch looks out over Bucharest.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

An abandoned NSA listening post on Berlin's "Devil's Mountain."

A castle from the Holy Roman Empire that hosts traveling youth... in its stables.

This abandoned coliseum was intended to be a grand Nazi rallying ground before it was halted at the end of the war.

This former quarry is now a picturesque gorge that hides a sunken lake.

The deepest sinkhole in Central Europe comes with a grisly tale and an unusual nickname: “The Stepmother Abyss.”