Built to defend Washington D.C. during the Civil War, this fort became a post-war nucleus for a thriving Black community.

This rare triple-jurisdiction drawbridge passes through Virginia, Maryland, and Washington, D.C.

America's first federal monument.

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

Helen Keller once broke ground on this historic center for the study of technologies to benefit the hearing impaired.

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

Washington's iconic carousel has a nice piece of Civil Rights history.

Home to a vast and influential collection of Shakespeareana.

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

Perhaps the most scandalous statue of America's first president.

The oldest continuously operating fish market in the United States.

The national park was once a plantation estate.

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

It was once the base for a series of domestic terror attacks.

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

The fine fabric handwoven at Biltmore Industries was once coveted around the world.

The enormous 250-room Vanderbilt mansion conceals hidden doors and secret passageways.

A wonderful display of arts and crafts handmade by local artisans in the Southern Appalachians.

The U.S. Supreme Court's secret Cold War relocation facility in the mountains of North Carolina.