Secret North Korean passage discovered below the world's most dangerous border.

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

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

Obscure Freemasons still live in D.C.’s largest private residence.

Home to items never before seen by the public.

The mirrored section takes the shape of Hebrew characters when viewed from above.

A retrofuturistic art installation in the Pittsburgh Airport.

The site of the little-known Pennsylvania battle that sparked the Seven Years' War.

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

Pennsylvania's highest point is spotted with boulders which were pushed to the surface by nothing but cold.

Behold the rickety glory of one of the oldest roller coasters still standing.

This shrine to McDonalds' most iconic sandwich holds a 14-foot tall burger.

A local prank turned town icon.

This Pennsylvania cave holds evidence of the oldest known inhabitants of North America.

This elaborate towering structure was once famed for its revolutionary height.

The house that Frank Lloyd Wright "(shook) out of his sleeve at will" at the age of 86.

One of the steepest streets in the United States makes an intriguing challenge for cyclists.

This charming colonial alleyway is one of the oldest continuously used residential streets in the U.S.

The world’s first penitentiary, meant to be humane, drove men insane.

The largest clock face in the United States is twice the size of Big Ben and infinitely more ad-sponsored.

The last funhouse of its kind, where guests enter through the mouth of an 80-year-old blue whale.

A piece of baseball history is preserved in a Pittsburgh parking lot.

This quarter-mile tunnel under the Bluff in Pittsburgh bends at a 45-degree angle.

An imposing pair of sphinxes stand guard outside this Egyptian Revival tomb.