This 17th-century street hidden beneath Edinburgh was once a breeding ground for the black death.

A labyrinthine underworld of tunnels and caverns hides beneath the city.

Dublin's most modern, visually spectacular bridge is modeled after Ireland's national emblem.

This massive monument has been telling the time for 150 years—at a slight angle.

These engineering masterpieces are a dominant feature of the Belfast skyline.

A giant sculpture of the legendary "Salmon of Knowledge" celebrates the return of fish to Belfast's River Lagan.

A museum marks and documents the site of the Titanic's launch.

The ship built to ferry passengers and goods to the doomed Titanic is now the last remaining White Star Line vessel.

The elaborate clockwork contraptions in this Scottish gallery create small worlds of whimsy and horror.

Christ's blood allegedly preserved in a Belgian town.

A sculpture of a famous ape who was once a beloved household name in London.

On the eve of a condemned prisoner's death, this bell rang 12 times outside their cell.

A stunning Victorian abbey and walled garden on a lakefront.

Head underground and take a tour of the city's working sewer system, and see the underground river Senne, which defined Brussels for centuries before being covered in the 19th century.

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

One of Amsterdam's narrowest houses is located right across the canal from its widest.

An Amsterdam street lined with antique shops each one dedicated to a different obscure collection.

Experience what life was like in Ireland during the Viking and medieval ages.

One of Ireland's most infamous prisons for rebels including men, women and children.

A museum that cashes in on its infamous little people while teaching you a thing or two about the Irish fey.

The only royal palace on U.S. soil has been a territorial capitol, a military headquarters, and a prison for a queen.

A Hawaiian stairway to heaven—that you can't climb.

Race through the maze, get your name on the sign.

Hide from the tourist hordes in these relatively unknown, and unguarded lava caves.