This massive swimming pool is the high tech home to the human-powered submarine races.

Remnants of a storybook amusement park hidden behind a strip mall.

This former asylum for Black Americans is haunted by its history of violence and racism.

A cave on the Maryland border where civilians took refuge during the bloodiest battle of the Civil War.

A hidden alley in urban Baltimore is a haven for graffiti artists.

Despite violent work crews and massive delays this abandoned canal tunnel was built to last into the modern day.

An astounding collection of medical specimens, including bits of President Lincoln.

Crammed into a Baltimore row house is an oddities shop that sells everything from skulls to dead insects.

Where the U.S. government kept its actual treasure, before Fort Knox.

The first presidential bomb shelter was located in an old vault under the Treasury, connected to the White House via tunnel.

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.

The site of the climactic scene from the classic horror film is now a historic landmark.

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

The hidden offices underneath Memorial Bridge have been locked up since 1976.

An eccentric company offers eccentric millionaires the opportunity to have spaceflight-related experiences.

An 18-mile-long tunnel for sewage waste will soon wind within the bowels of Washington, D.C.

Remains of a historic fountain that was mysteriously lost in the demolition of a D.C. traffic circle.

Hear, smell, see, taste, and touch history at this immersive Civil War hospital.

The FBI's urban training course may have the highest fake crime rate in the world.

Giant busts of 42 U.S. presidents are sitting in a field in Virginia.

The remnants of a wooden-hulled fleet built and abandoned in WWI, now home to a thriving ecosystem.

This abandoned asylum was once a state of the art facility before devolving into one of the most deadly mental institutions in American history.

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

The haunting "Hell House Altar" is one of the few remnants of an abandoned college that has been a magnet for local legends.