This massive subterranean fissure is known as the "underground Grand Canyon."

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

A star-shaped fortress town fort built in the geometric model of the Renaissance utopian city.

This abandoned coliseum was intended to be a grand Nazi rallying ground before it was halted at the end of the war.

This centuries-old tree tells an unusual tale of vegetation and fertility in the desert.

A trough of 700 strange bronze faces runs through a narrow alley in Ljubljana's old town.

Peace Park and the Atomic Bomb Dome.

Nine Gardens in one—with tea service.

Japanese national treasure originally built in 593 CE.

This isolated Japanese mountain village untouched by time showcases unique and stunning traditional architecture.

These upturned herring boats make nifty storage sheds for fishing goods.

Men in rubber-soled boots serve as your "brakes" on this toboggan ride Hemingway described as "exhilarating."

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

Dublin's "Dead Zoo" serves as a window to Victorian museum design.

The comedy and tragedy of Oscar Wilde is preserved in a Dublin park, captured in a sculpture of colorful stone.

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

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

The beautiful baroque library of the Hapsburg empire.

Famously misunderstood wonder of the ancient world

The fairy tale castle of the "fairy-tale king."

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.