These recently uncovered walls are all that's left of Washington, D.C's first defense contractor.

This train station inspired the name of a 1970's rock band and provided the backdrop for their album cover.

The Aldie Gristmill was once the largest factory of its kind in Loudoun County.

The only surviving 19th-century water-powered mill found in the Washington, D.C. area.

An echo chamber with a waterfall wrapped around its base at the Embassy of Canada in Washington, D.C.

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

This museum sits on the site of a decommissioned military communications base.

This pre-Revolutionary War grist mill ground corn and flour for soldiers in seven American wars.

Originally dubbed "Retirement" by the Navy Commodore who built it in 1780, this beautiful mansion is now the centerpiece of a suburban community park.

Home to a 27 room house, this estate was crafted by Black entrepreneur Olander Banks Sr.

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

There’s a hidden military meme engraved on the World War II Memorial.

A replica of the famous memorial statue at the Normandy American Cemetery hides in an office building in downtown D.C.

One of the oldest active carousels in the country—but it might be missed by all but the keenest-eyed boardwalk strollers.

This building at the south end of the boardwalk was once home to the U.S. Life-Saving Service and the U.S. Coast Guard before being rescued itself.

This one-room schoolhouse played a significant role in the education of Black children for almost 100 years.

The stone marker that Mason and Dixon placed at the eastern end of the famous north-south border they surveyed.

This 1830s store is believed to be the site of Harriet Tubman's first stand.

The United States' oldest Episcopal church still in active use.

Historic home of America's sweetheart sharpshooter, Annie Oakley.

The elevator hidden in a smokestack on Roosevelt's yacht now serves as a monument to the former president.

One of the earliest and best-preserved buildings in Charles County, Maryland.

This homestead was occupied by Union soldiers, who believed the owners were signaling Confederate forces.

The last early 20th-century schoolhouse in Fairfax County has galvanized the community and engendered a spirit of service among residents.