A former major munitions plant that has been converted into a sprawling art space.

The last holdout of a pre-Civil War rebel who took the matter of slavery into his own hands.

The semi-reclaimed ruins of this canal were once part of an ambitious plan to reroute the mighty potomac.

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

This dramatic rail curve was once the target of a failed Nazi attack.

This university transit system is a 1970s vision of the future.

A model of a dinosaur that was named for Andrew Carnegie stands outside the museum that also bears his name.

The largest university building in the West is a gothic masterpiece containing dozens of theme rooms based on different countries.

There aren't too many operational funiculars around, but Pittsburgh has two!

The world's tallest doric column is this Ohio monument to a naval victory in the War of 1812.

This massive airship factory is so large that it has its own indoor weather.

A flamboyantly decorated bridge signals diversity and fellowship at the entry to Indianapolis' Broad Ripple Village.

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

This "floating railway" is one of the world's oldest monorail systems.

Once decrepit and slated for demolition, now one of the longest pedestrian bridges in the world.

When you visit his grave, be sure to rub the Great Emancipator's nose for good luck.

These powerful, if squat, Canadian waterfalls flow in different directions depending on the time of day.

The world's longest known cave system.

A toxic ghost town sitting atop a massive coal fire.

The ruins of this Dutch castle sit atop a labyrinth of once-secret tunnels and passageways, dating back over 900 years.

An indoor miniature village and labor of love for Laurence Geiringer, a model railroad enthusiast.

A dramatic, 360-degree recreation of Pickett's Charge in the Civil War.

The farm where one of America's greatest leaders was raised is now a well-appointed landmark.

The hotel where Martin Luther King Jr. was shot is now a museum dedicated to his work.