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

This petite park lets visitors see and touch examples of fossilized dinosaur tracks.

A nuclear bunker built to shelter the politicians and important people of Scotland in case of nuclear attack.

Built to hold the worst of the worst of the Nazi war prisoners.

Protecting the dead from opportunistic body snatchers.

Ruined castle with subterranean vaulted Goblin Ha' or "Goblin Hall."

Wallabies live naturally on this Irish island.

The ancient tomb acts as a calendar that keeps perfect time.

Perfectly preserved ancient monastery in an impossibly dramatic location on a rocky island in the Atlantic.

Charles Babbage's proto-computer, painstakingly brought to life.

Rebuilt remains of a temple to Roman god Mithras.

The only university zoological museum in London houses extinct animals, bizarre natural history specimens, and a Micrarium of microscopic creatures.

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

Underground hospital complex constructed by slave laborers during the German occupation of the Channel Islands.

An intricately decorated tiny place of worship.

Grotto replete with mystical designs laid out in glued shell mosaics.

Huge concrete structures designed as an early warning system for Britain to detect enemy aircraft.

This foolish Victorian sea fort was converted to a deluxe hotel.

Museum about life, death, and cannibalism in the Stone Age.

Rare collection of medieval books under lock and key.

A perfectly running 230-year-old silver automaton and music box.

The final resting place of American icon Buffalo Bill, and a museum that aids in telling his tale.

At Chicago's revered Field Museum, visitors are invited to learn about and literally explore DNA.

A small horde of mythical creatures lurk almost imperceptibly within the museum's wildlife dioramas.