What was once the second largest steel mill in the US is now a sprawling complex of modern ruins.

World's second largest particle accelerator, where nature reveals its secrets.

A replica viking ship from the Chicago World's Fair is still in dry dock in an Illinois park.

Home to the world's largest refracting telescope and the birthplace of modern astrophysics.

Arguably the best example of an authentic Dutch windmill in the United States, rivaling its counterparts in the Netherlands.

A hidden grotto on the grounds of the Kane County Government Center.

A creepy sculpture of a decapitated head invites viewers to see St. Louis through its empty eyes.

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

Oversized statues are just the tip of this nostalgic Americana roadside attraction.

A museum of the dime museum that features weird entertainments of yesteryear, from feejee mermaids to flea circuses.

A theme park attraction designed to turn your children into LARPers.

A late sculptor's last project was to turn this abandoned cement factory into a castle-themed amusement park.

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

Every winter, the wind carves blocks of frozen water into beautiful abstract shapes inside this unusually curved tunnel.

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

This cave holds a surprisingly colorful variety of geological oddities.

Entombed in this strange, white stone hill are the deadly remains of radioactive weapons production.

A bizarre house filled with an astounding array of collections.

The maximum security facility was once thought to have "the bloodiest 47 acres in America."

A remote hill on a stretch of country road where the laws of physics are defied... or so it seems.

A rainbow-colored house promotes LGBTQ rights across the street from the Westboro Baptist Church.

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

The quirky collection includes treasures like Elvis' underwear, Bob Barker's toothbrush, and hundreds of sock monkeys.

This historic cliffside mansion uses a natural cave for air conditioning.