On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

The magic's in the hole!

The only castle in North America to ever house European sovereigns.

Go inside to really appreciate this 500-year-old technological masterpiece.

A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

2300-year-old Roman road connecting the empire.

Breathtaking and huge 430 year old maps of Italy.

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

Cold war icon and onetime "hole" in the iron curtain.

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

Macabre astrological automaton clock dating to the late 1400s.

A beautifully eclectic mix of architectural styles.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

Founded as a refugee camp, now a popular tourist spot.

One of the few remaining ancient aqueducts described by Frontinus as 'the most solemn testimony of the Empire.'

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

An ancient Egyptian temple in the middle of Madrid, Spain.

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

The world's largest wooden structure.

The final resting place of the great navigator, or maybe his brother.

A once-glowing grotto at the bottom of Waikapalae Wet Cave.

This blowhole is supposedly caused by a trapped monster.

One small town in the Pacific Northwest transformed itself into a Bavarian-themed tourist destination.

Cave carved out of a huge snow drift collapsed killing one and injuring five in July 2015.