There's a crumbling old mansion inside the Smithsonian National Zoo.

This fort down the Potomac from Washington, D.C. was once the only defensive fort protecting the capital.

Standing for over 200 years, the abandoned home of a Revolutionary War hero and later a succession of prison superintendents.

A suburban museum tells the story of a historic transportation network and even provides rides in antique trolley cars.

A mammoth pair of Civil War artillery guns abandoned out in the forest.

The United States Capitol's former columns still stand.

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

The U.S. Navy’s preposterously detailed mini battleship took 77,000 hours to complete.

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

Part of a WWII submarine is lurking outside the Washington Navy Yard parking lot.

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

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

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.

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

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

Ride in 1960s style on the private luxury train Marshal Josip Tito used to travel around Yugoslavia.

The span is crooked and made from two older recycled bridges.