The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

This abandoned prison castle has become an imposing gallery of graffiti art.

Community bookshelf of 25-foot-tall book spines.

400 million-year old limestone caverns nestled in the Ozarks served as shelter and a hideout for cultures throughout North American history.

A historic house in St. Louis was plagued by a series of suicides committed by family members involved in a successful brewery.

Curious cave that stays a cool 56 degrees all year long.

The world's largest man-made underground caverns offer unparalleled underwater wonders.

The history of the treatment of mental illness, illustrated in all its gory detail, and housed in an asylum.

Erosion and time have created a naturally-formed water park.

Once an ambitious nature spa, these forest ruins now provide a serene monument to failure.

European castle ruins in an American state park are actually the product of death and grief.

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

Urban explorers embraced America's now demolished first suburban mall, south of Chicago.

Huge abstract sculptures of the Puerto Rican Flag.

A 30-foot man on a penny-farthing bicycle rides along the banks of the Mississippi.

It was originally part of a "terrible lizards" collection at the 1964 New York World’s Fair.

You can take a class, browse the library, or visit the lavish lair of an international men's humor society.

Illegal drag racing two stories beneath Chicago’s streets.

The clothes-washing king doubles as a community center with some unusual features, including an aviary filled with finches.

This historic Illinois "Muffler Man" has been converted from axe-touting lumberjack to rocket-wielding space ace.

Theater has had many different incarnations but has survived the ravages of time.

The 40-year-old machine serves soda quicker than you can catch it for a mere 75 cents a pop.

An amazing collection of scale model ships.

Man-made geyser that rises to the exact height of the Gateway Arch.