No one knows how many bodies are in this vault in a Chicago public park.

This national park dedicated to the tallgrass prairie ecosystem still displays its military past.

A monument to the art of slicing people open.

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

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

This alley in downtown Chicago held the bodies of over 600 people after the fateful Iroquois Theatre fire.

A gothic church spire sits atop this skyscraper, the tallest church in the world.

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

This cheerfully-named branch of the Chicago River is the fetid result of years of blood, entrails, and meatpacking waste.

An outdoor urban gallery of large-scale artworks by the world's most influential street artists.

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

Former meatpacking facility turned vertical farm and sustainable business complex.

Dating back to the 1800s, two imposing buildings in Michigan have had countless transformations over the years.

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

An abandoned relic of the city's failed experiment with below ground transit.

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

A 19th-century horse lover's bequest led to the construction of this unique fountain in Chicago.

A stunning, abandoned limestone quarry in southern Indiana provided the stone to erect the Empire State Building.

Tucked away in the forests of Indiana resides an abandoned waterslide that is now a popular graffiti haunt.

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

This urban drawbridge gained eternal pop culture fame when the Blues Brothers jumped it while it was raised.

This museum remembers an apocalyptic cult that became more famous for baseball than religious radicalism.

The remains of a religious colony, its amusement park, zoo, and baseball empire.

In an alley not far from where two great highways meet, byways of a very different sort are honored.