An important landmark in the history of algebraic logic.

A proud bronze billy stands as an eternal symbol of Ireland's oldest festival, where a goat is made king.

This 30-foot pile of rocks may be the grave of a mythological Irish queen.

A tiny microvalley etched into the side of Knocknarea Mountain hides another world.

You can see three Irish counties from this Neolithic hillside fort, once the seat of the Kingdom of Ailech.

A massive Celtic cross secretly growing in an Irish forest.

The ruins of this medieval castle in Northern Ireland have inspired artists from C.S. Lewis to Led Zeppelin.

Northern Ireland's Brobdingnagian stepping stones.

This short bridge is the only thing connecting a tiny Irish island to the mainland.

The atmospheric road was never meant to be so creepy.

The tomb of one of Scotland's bloody historic villains is a magnet for bumbling desecrators.

Protecting the dead from opportunistic body snatchers.

The 16th-century church has the only stained glass windows that survived the Scottish Reformation intact.

Overlooked by many, the two famous Scottish warriors guard the main gate of Edinburgh Castle.

The fountain marks the area where hundreds of accused witches were burned at the stake.

The final resting place of soldiers' loyal canine companions.

A sweet symbol marks the place where torturous executions were once carried out.

A statue in the heart of Edinburgh honors a bear that served in the Polish military during World War II.

Remnants of the 16th-century defensive wall still stand unassumingly within Edinburgh.

This monument to one of the largest science fiction games of all time bears the names of hundreds of thousands of players.

An encyclopedic collection of mammal penises.

Iceland's largest geothermal mud pool is a little bit haunted and a little bit dangerous.

Medicinal spa created with the discharge from a geothermal energy plant.

This stunning concert hall has become a symbol of Iceland's national recovery.