This outdoor gallery of graffiti-covered walls pays homage to the past, present, and possible future of street art.

A crumbling hospital from the 1850s on Roosevelt Island.

Once a dumping spot, now a park with a kayak launch.

A drawbridge named for a potentially intersex Polish national who fought alongside George Washington during the American Revolution, and an example of "Pulaski Red".

Elevated freight railway turned wildly successful urban park.

Once a ferry dock, radio transmitter, and now a new Greenpoint park.

Try not to get slimed in Tribeca.

Andy Griffith's hometown has made itself up to look like the fictional town of Mayberry.

America's post-nuclear-attack chambers of Congress.

Once connected to the outside world by a single train track, this ghost town is looked after by the National Park Service.

An office built to look like a giant basket.

The world's longest known cave system.

A turn-of-the-century architectural marvel built on healing mineral springs and salt licks.

A singular collection of hand-built art deco cars are held in a building with style to match.

A store full of vintage and indie toys designed to bring out the kid in even the crustiest of adults.

One part antique store, one part curiosities hodge-podge.

An emerald-green grotto just a short trip from Austin.

A castle built by an eccentric medieval enthusiast in suburban Ohio.

The world's largest collection of mechanical puzzles is a cornucopia of analog bafflers.

These grassy undulations on a stretch of University of Michigan campus aren't bad landscaping, they're art.

The fifth-longest suspension bridge the world, connecting one Michigan peninsula to another.

Island where motor vehicles are banned -- home to the only carless highway in the United States.

One of the largest crucifixes in the world stands 55 feet tall in a secluded, wooded area of northern Michigan.

The body of one of the world's most famous outlaws is covered in cement and iron to prevent it from being stolen.