The palatial McDonald's that inspired Wesley Willis.

A little-known subterranean street runs under some of the best-known buildings in Chicago's River North.

A century-old network of freight tunnels underneath the city's historic business district.

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

This historic hotel invented the chocolate brownie.

A Museum of Holography frozen in 1974.

A lush green oasis in the middle of Chicago.

A former atom smasher turned into an art gallery.

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

Pumpkin-like gargoyles and grotesques peer down from the rooftop of this unassuming apartment building in Illinois.

This house renovated by Frank Lloyd Wright was the centerpiece of a lavish 20th-century estate.

To find the "unicorns of the deep" you've got to go downstairs.

Where dioramas can follow you home.

One-of-a-kind preserved ruins of an abandoned 1880s church in Chicago's Pilsen neighborhood.

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

These abandoned grain silos and tunnels are an urban exploration dream.

Tucked away amongst townhomes lies a restored, early 20th-century tea house and garden, the only remains of a historic estate.

This historic-shipwreck-cum-diving-spot can still be seen poking its boiler out of the Lake Michigan waters that claimed it.

Former meatpacking facility turned vertical farm and sustainable business complex.

What's left of the ruins of the 1893 Columbian Exhibition, or World's Fair, also known as the White City.

An avant garde art museum at the University of Chicago.

This modest post office sits on the site of H.H. Holmes' famous murder castle.

A small abandoned and abused cemetery that has become a magnet for ghost hunters.

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