The United States's largest hand-dug well is topped with a state-of-the-art museum.

The modern birthplace of Irish freedom.

The world's toughest modern Christian pilgrimage leads directly to the gates of Hell.

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

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

A mining town once rife with murderous disputes over its copious treasures now creates income as a popular spot for photo shoots.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

Venice's "Island of the Mad."

An unusual round church in London with a Templar past.

The world's longest known cave system.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

A reproduction of earth's many biomes.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

A beautiful geyser under environmental threat.

The oldest cemetery in New Orleans, resting peacefully for over 200 years now.

Standing in a state of "arrested decay," this ghost town allows for a detailed peek into Gold Rush life in an unusually harsh climate.

The final resting place of New Orleans' most famous voodoo priestess.

France's most famous cemetery, with some of its most curious tombs.

Aqueducts have dramatically changed this old lake, now home to tufa towers and its very own species of tiny brine shrimp.

Northern Ireland's Brobdingnagian stepping stones.

The first declared National Monument in the United States.

A battle between nature and architecture in the Cambodian jungle.

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