A bizarre roadside attraction and the first instance of miniature golf in the world.

The largest self-built castle in the U.S., six decades in the making.

A castle built by an eccentric medieval enthusiast in suburban Ohio.

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

Less a museum than a bizarre fantasy world created by artists and engineers.

A hidden network of subterranean passageways lies tangled beneath Indianapolis' bustling City Market.

Home to items never before seen by the public.

The world's longest known cave system.

The largest earthwork effigy in the world.

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

An acoustic anomaly with a mysterious cause sits in the heart of Tulsa.

Possibly the most beautiful carillon in the world, set atop Iron Mountain in Florida.

One person’s lost luggage is another person’s treasure.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

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

The first declared National Monument in the United States.

Famously misunderstood wonder of the ancient world

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

A bizarre house filled with an astounding array of collections.

The world’s first penitentiary, meant to be humane, drove men insane.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

This tipsy office building in downtown Prague was originally called “Fred and Ginger.”

Macabre astrological automaton clock dating to the late 1400s.