A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

The Pope’s secret escape route.

Climb inside an iron crystal magnified 165 billion times its normal size.

This lovely, if imposing, piece of Canadian gothic is possibly the most photographed hotel in the world.

Giant topiary dog once played a role in a terrorist bomb plot.

A statue of a boy looks up at where the famous rival to the Leaning Tower of Pisa once stood.

Holy Grotto of Montserrat Monastery holds one of Europe's mysterious black Madonnas.

A Black Forest cuckoo clock theme park features one timepiece big enough to walk inside.

A memorial to the nearly 10,000 American soldiers laid to rest on the beaches of Normandy during WWII.

This enormous "cloth of the conquest" depicts the Norman invasion of England in mind-blowing detail.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

A neighborhood church's unusual abstract stained glass was the final project of avant-garde artist Jean Cocteau.

Breathtaking and huge 430 year old maps of Italy.

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

This ritzy Italian market is built around a statue of an unforgiven heretic who was burned for his belief in an endless universe.

Climb to the top of this windmill for a scenic panorama and up-close look at wind energy production.

This eye-catching roundabout sculpture commemorates one of England's best World War II-era "shadow factories."

The obelisk honors the cyclist troops who were killed during World War I.

These crude contraptions were used to aid in the mining of lead, silver and gold.

Several land speed world records were shattered at this Welsh beach.

These barriers stand as stark reminders of Northern Ireland's troubled past.

For over 500 years this timbered alms house has provided a home for elderly residents of Coventry.

A typographic tribute to the many comedic greats who make Great Britain laugh.

World's largest working waterwheel has been around for over 150 years.