The ruins of a world-renowned medieval hospital.

This harrowing climb along West Virginia's jagged spires is one of the only Via Ferrata on America's east coast.

One of the last Jazz Age "Wonder Theaters" in New York City.

You might recognize this historic Oregon mansion from its appearance in 'The Goonies.'

The ruins of a defunct limestone quarry still haunt this Scottish promontory.

The ruins of a 15th-century tower house.

A journey begins with a single step, and for many, the road-trip of a lifetime started at this Chicago intersection.

A rare example of a Lowland broch.

Believed to be the capital of the the ancient kingdom of Dál Riata.

The ruins of a once-grand castle that played host to a tournament with 100,000 attendees.

Carved between 3500 and 1000 B.C., the distinctive carvings at this site are poorly understood.

An unrealized dream to wirelessly electrify the entire Earth.

A beautifully-carved Pictish stone encased in a protective glass structure.

According to local legend, this church was built with two doors, so that residents of two rival villages had their own entrances.

Once used as a deterrent to drinking alcohol.

A mosaic map made of over 100,000 tiles depicts the geological features and sea creatures that live along this San Diego beachside community.

The Devil’s Porridge tells the story of HM Factory Gretna and the munitions girls who mixed deadly chemicals.

This ancient gaming tool was unearthed during the construction of this former town's central square.

An approximately 500 million-year-old rock outcropping covered in fossilized bacteria.

The final resting place of Gary Gygax; co-creator of Dungeons and Dragons.

A pair of stone circles positioned on the bank of the River Esk.

In use from 1742 to 1910, only flat headstones were allowed in this cemetery.

A monument to an Irish secret society thought to be responsible for a string of violent attacks in Pennsylvania coal mines.

A church that bred legends, and served as an inspiration for the Da Vinci Code.