The world's longest known cave system.

Community bookshelf of 25-foot-tall book spines.

Once one of the world's great cities, Cahokia was a place of religious worship, trade and mass human sacrifice before being mysteriously abandoned.

The world's smallest drawbridge.

Oldest synagogue in the United States.

Paths are maintained, but trees have taken over plots.

Macabre headstones carved with winged skulls, dancing skeletons, and pithy reminders of impending death.

This 38-drawer structure claims the superlative title, but it isn't the world's only giant filing cabinet.

This inexpensive lodging house was once a prison notorious for its inhumane practices.

Futuristic apartment blocks are the backdrop for Montreal surfers hangin' ten on the Habitat '67 standing wave.

Trade in that pesky human soul for cold-hard circuits.

Nonprofit art center that promotes outsider, intuitive, and self-taught art.

The 80-foot tire that looms over Michigan's I-94 was once a Ferris wheel in the New York World Fair.

One man's attempt to create an artistic wonder on a run-down block in Detroit.

Standing guard on top of an old, vacant ice cream shop.

Detroit’s downtown castle is one of the oldest structures in the city.

Advice-columnist's bell tower, paid for with pennies.

38-story baroque tower reflecting Detroit's rise, fall, and possible rise again.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.

Statue dedicated to the star of an old television show.

A place to eat for on-the-run agents and espionage enthusiasts.

Half-sized replica of the Leaning Tower of Pisa built to honor Galileo.

A river with some unusual, and occasionally dangerous, habits.

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