A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

An overlooked memorial honoring the local Washington residents who died in World War I.

A hidden passageway now marks the site of an assassination attempt on Ronald Reagan that some say broke a 140-year-old curse.

A portal into the bricked up canal that runs through the heart of Washington D.C.

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

Was there a small "backpack nuke" hidden in the attic? JFK apparently thought so.

The preamble to the U.S. Constitution written entirely from vanity license plates hangs in the Smithsonian museum.

During Prohibition, the U.S. Congress had an "official" bootlegger, with his own Capitol Hill office.

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

This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.

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

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

Behind an abandoned storefront is an example of pioneering 1930s gas station architecture.

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

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.

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

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

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

"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!”

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

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