Beneath the impressive baroque cathedral that rises from the center of Berlin lies the largest collection of Prussian royals in the world.

Super-heavy Nazi architectural experiment.

A 12th-century fortress containing some of Berlin's oldest buildings.

A tree-like building perches on its trunk in the Steglitz neighborhood of Berlin.

The site of the famous Nazi book burning campaign of 1933 remembers its "Night of Shame".

The bunker where Hitler took his own life is hidden under this deliberately ordinary parking lot.

A fascinating insight into daily life in the Eastern Bloc.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

A wunderkammer of mysterious objects and stories.

A slice of central Asia in the middle of Berlin.

A section of the long chain that blocked enemy ships from entering Constantinople.

This half-forgotten fortress was constructed by the Ottoman conqueror of Constantinople.

This former Imperial summer home was the venue for a royal slap that once echoed 'round the world.

The legendary luxury train passage is commemorated with a charming museum inside its former eastern terminus.

This column celebrates Rome's victory over the Goths, and may be the oldest Roman monument in Istanbul.

One of the largest wooden constructions in Europe was meant to be a casino, but soon became an orphanage.

No one is sure if the world's fourth-largest diamond had been found in a rubbish heap or was pawned by Napoleon's mom.

A gorgeous, Gaudí-esque stairway constructed in the city of Istanbul by a prominent Jewish family.

This crucial gathering spot along the "hippie trail" still displays old notes between traveling beatniks and backpackers.

A fountain standing as a testament to a doomed alliance.

Ancient serpentine sacrifice holder that has stood the test of time.

Climb a steep hill in 90 seconds on the second-oldest urban subway in the world.

A sixth-century Byzantine cistern hidden below a modern carpet store.

Large miniature theme park with 100-plus models.