The longest navigable underground river in the United States is home to countless blind and albino animals.

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

This quirky curiosity shop takes its cues from the world's bazaars.

A speakeasy takes on Chicago's drinking culture.

A giant bronze coil of feces is both a tribute to doggie defecation and a reminder to pick it up.

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

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

Former meatpacking facility turned vertical farm and sustainable business complex.

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

One of the largest pieces of scientific equipment ever carried on a NASA space shuttle sits in a Chicago alley.

This bronze sculpture on a former squash court marks the secret origins of the Atomic Age.

An actual 1957 Cadillac De Ville, encased in 15 cubic yards of concrete.

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

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

This former Indiana quarry has been transformed into a park and SCUBA site where divers can explore the drowned mining equipment.

The Kalamazoo factory has 100 years of instrument-making, and one big wartime secret.

This old steel industry company town has a tradition of parking cars on the sidewalk so people can walk in the narrow streets.

This stunning gothic ruin was a casualty of the Indiana steel industry crash.

This bridge was constructed from the remains of the first Ferris wheel.