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

Before Nixon, "watergate" meant canals.

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

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

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

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

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

A museum cafe showcases Native American dishes and indigenous ingredients from across the Western Hemisphere.

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

An overlooked oasis of quiet on the grounds of Washington's monumental basilica.

A traveling postal dog covered 48 states and more than 140,000 miles, and he lives on as taxidermy, patched up with a rabbit's foot and a pig's ear.

The most accurate timepiece in the world.

Perhaps the most scandalous statue of America's first president.

Decades before the scandal, this staircase on the river was a literal "water gate."

A celebrity from the late Cretaceous period.

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

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

Largest Roman Catholic church in North America.

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

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

The national park was once a plantation estate.

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

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

The winding route passes through an enclosed alleyway, two tunnels, and leads to the White House basement.