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

The elevator that makes it possible to fly American flags in bulk over the U.S. Capitol

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

Soldiers were buried next to Lee's house in the center of Arlington Cemetery to dissuade the general from reclaiming his property after the war.

The controversial urban planner who designed Washington, D.C., was buried in Maryland, and can presently be found in Virginia.

Need a hardcopy of the 50-title Code of Federal Regulations? This is the place.

The only National Monument ever to go missing for nearly 50 years then resurface in a dump.

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

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

A muscular Art Deco monument represents the struggle between regulators and unbridled markets.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

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

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

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

Home to items never before seen by the public.

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

Look closely and you’ll notice that the color changes a third of the way up the tower.

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.

At 207 feet, one of the world's longest continuous escalators.

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

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

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