An ancient Scottish rock formation said to be the gravesite of a giant remains ensconced in legend and intrigue.

This single-track road rewards brave drivers with stunning Scottish scenery.

Swiss vineyards in a UNESCO heritage site.

Over 3km of caverns and caves at the Switzerland-France border contain the largest underground river in Central Europe.

This cramped crevasse saw the entire population of its island suffocated inside its depths.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

A cave dwelling that was started by the Celts, expanded by monks, and finished by knights.

Ancient paintings known as the "Sistine Chapel of Cave Art."

The abandoned mine where American troops discovered a treasure trove of art and artifacts hidden by the Nazis.

This ethereal, rainforest-like gorge is home to waterfalls, quaint bridges, and fairy folk.

A massive Celtic cross secretly growing in an Irish forest.

A carved bench marks the Scottish cave that inspired the classic adventure novel "Treasure Island."

This unusual rock looks like a giant, otherworldly mushroom sprouting atop a cave.

This controversial Irish show cave is home to a massive formation known as the Great Stalactite.

This tiny little cave was said to have been a refuge for a saint with a glowing arm.

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

This mysterious pig iron pillar does not rust, despite being weathered by the elements for centuries.

Traveling this mountain pass reveals quaint stone buildings, stunning Irish scenery, and a bridge said to grant wishes.

More stones than Stonehenge, all scattered within a windswept landscape sure to enchant 'Outlander' fans.

The one-time stronghold of the noble Douglas family, now home to ghost sightings and nesting birds.

Long abandoned underground complex to keep royals safe from a nuclear war that never came.

A meandering boardwalk across the bogland leads to a "stairway to heaven" with sublime views.

This series of Scottish caves has no clear purpose other than baffling historians.

This ancient Irish landscape boasts hundreds of legendary ruins.