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

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

A heroic pigeon that, through a barrage of gunfire, delivered a message that saved over 100 lives in World War I.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

A little marble compass above George Washington's (empty) tomb in the Capitol marks where D.C.'s four quadrants intersect.

Members of Congress have traveled between the buildings on Capitol Hill for a century hidden from tourists, press, and storm clouds.

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

The oldest continuously operating fish market in the United States.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

The house where John Wilkes Booth conspired with his co-conspirators.

There’s a hidden military meme engraved on the World War II Memorial.

The most decorated dog of World War I is preserved in the Smithsonian.

The first purpose-built art gallery in the United States is once again open as a center of craft arts.

The walls of the iconic dome are hollow and have a secret stairway.

A nostalgic bibliographic gem.