In which a local geological marvel becomes a quaint roadside attraction.

A gargantuan crystal kingdom.

It's believed a castle existed at this site since the 12th century.

Hidden in this little-known town stands a piece of agriculture history.

Irontown was founded in 1868, as a second attempt to mine iron from the nearby Iron Mountain.

Lost subway station nestled beneath Toronto's busy commuter line.

An optical illusion found amid a logged redwood forest.

An abandoned Yorkshire castle that is hidden in plain sight.

Ancient cave tombs known as the "houses of fairies."

A 2,000-year-old engineering wonder hides beneath an Italian town.

The world's longest known cave system.

This nondescript tunnel has been featured in a number of iconic movies, from “Roger Rabbit” to “Back to the Future.”

Old Danish castle immortalized in Shakespeare's Hamlet.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

Generations of rockhounds got their start at this beloved, historic mine.

The location where the iconic movie character declared it was time to go home.

These ancient sea caves hold Britain's highest concentration of Pictish rock carvings.

This fortified L-shaped tower is the ancient seat of clan Hannay.

The hallowed remains of a 900-year old Ancestral Pueblo great house.

Is this a portal to another side of the cosmos?

Believed to be the birthplace of John Balliol.

Incredible labyrinth of man made caves.

Turtles swim in a pond surrounding a classical temple in this lush park in Vicenza.

Rediscovered after a century, the father of the American Navy was reinterred in something dredged up from Davy Jones' Locker.