Some of the tallest ancient American ruins continue to inspire awe and curiosity.

This Arizona observatory is famous for investigations into Martian life, and as the place humans first spotted Pluto.

Ancient pueblos built into the base of a natural canyon wall.

A pair of giant roadside arrows are all that remains of a former Route 66 trading post.

Northern Ireland's Brobdingnagian stepping stones.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

A cluttered and astounding collection of antiquities and curiosities.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

The fairy tale castle of the “fairy-tale king,” this was also the inspiration for Disney’s “Sleeping Beauty.”

A museum wholly devoted to juvenescence.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Macabre astrological automaton clock dating to the late 1400s.

The last holdout of a pre-Civil War rebel who took the matter of slavery into his own hands.

This Prague museum collects brutalist relics and memories from the country's former Soviet rule.

The Grand Ole Opry's big voice came from a small home in rural Virginia where she was eventually buried.

Monument to a suicide protesting the Soviet invasion.

Buried five stories underground, this Soviet bunker is packed with gas masks and Cold War paraphernalia.

A church of bones, decorated with 40,000 human skeletons.

A 98-room castle in the middle of Toronto that bankrupted a 19th century electricity multimillionaire.

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

This stately building in Alexandria, Virginia was built by Freemasons to honor one of their most famous members.

America's Most Wanted's set resides in this tribute to the history of crime and punishment.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.