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

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

Home to a vast and influential collection of Shakespeareana.

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

The fountains of the U.S. Navy Memorial are annually salted with water from the Seven Seas as part of a nautical ritual.

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

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

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

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

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

A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.

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

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

100 years later, they're still down there.

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

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

One of the largest artillery pieces in the world sits in a Washington D.C. parking lot.

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

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

A historic arena where the Beatles played their first concert in the U.S.

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

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

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

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