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

A diminutive memorial marks the site of a successful assassination by a right-wing death squad in America's capital.

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

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

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

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

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

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

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

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.

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

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

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.

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

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

The discovery site of the "Capitalsaurus," the official dinosaur of Washington, D.C.

This unacceptably tall building was the real reason for Washington, D.C.'s skyscraper ban.

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

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

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

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.