The early data processor factory founded in Washington for the 1890 U.S. Census went on to become IBM.

This nine-story building is the oldest standing skyscraper in D.C.

Before Metro, Washington had a robust streetcar network—and you see the remains of this infrastructure if you know where to look.

The school tested mustard gas for the U.S. Army during World War I.

They sort through millions of dollars worth of diplomatic gifts on behalf of the government.

Before founding the American Red Cross, Clara Barton had a tremendous humanitarian impact by locating thousands of missing soldiers.

Daredevil repair workers can worm their way out the access hatch, loop ropes over the apex and rappel down the monument.

Helen Keller once broke ground on this historic center for the study of technologies to benefit the hearing impaired.

There just so happens to be a court even higher than the U.S Supreme Court: a basketball court in the building itself.

When it comes to handsignals (and colonialism) rock always beats scissors.

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

100 years later, they're still down there.

There's an old indoor swimming pool hidden directly underneath the White House Press Briefing Room.

This forgotten boat elevator was an engineering marvel in its heyday.

Washington's top-secret Cold War-era doomsday communications tower is located in a small neighborhood park.

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

A building shaped like the Army Corps of Engineers logo, because why not?

A diminutive plaque recalls the treetop sniper who almost killed Abe Lincoln.

There’s a special club house at the top for the bell ringers.

This stately mansion, built in 1787 by America's first Secretary of the Navy, is rumored to be one of the most haunted buildings in Washington, DC.

Senators used to relax in the nearly forgotten marble tubs now hidden in the U.S. Capitol Building's basement.

This robust fence in front of a historic Georgetown home is likely made from hundreds of recycled Revolutionary War firearms.

A small triangle of DC grass is the final resting place of one of Sonny and Cher's songs.

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