Washington's iconic carousel has a nice piece of Civil Rights history.

The hidden offices underneath Memorial Bridge have been locked up since 1976.

The "lovely red Vega" of the legendary record-settling pilot.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

A mailbox that saved a nature reserve.

The land is home to swimming ponies and a legendary 18th-century treasure.

Pennsylvania's own Roswell-style UFO mystery.

A favorite of Amelia Earhart, ranking among those rare bridges that can be crossed without changing sides of the river.

Mussolini gave Cincinnati a bronze statue of Romulus and Remus suckling at a wolf's teats.

The largest earthwork effigy in the world.

Constant erosion has created a surreal landscape of bleached and preserved fallen trees.

An ancient system of freshwater caves filled with animal bones, including that of species long-extinct.

America's most famous museum of medical oddities is home to the remains of Albert Einstein's brain.