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

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

This lifelike sculpture of a policeman serves as a helpful reminder to watch out for crossing pedestrians.

Tom Thumb's carriage is among the highlights of this unique collection of horse-drawn vehicles, donated by a carriage connoisseur and tucked away inside beautiful Morven Park

The oldest surviving one-room schoolhouse in Montgomery County, Maryland.

These figures float and flutter in this fountain crafted by famed Swedish sculptor Carl Milles.

A remarkably well-preserved one room schoolhouse that dates back to 1876.

The largest cemetery for enslaved people in Loudoun County was almost lost to history, if not for the research of a minister.

This church is known as "The Home Church of George Washington and George Mason."

Marker for a long-gone electric trolley line that spurred the economic development of West Asheville.

A popular supernatural horror film based in this quaint Maryland village made it a destination for paranormal pilgrimages, but unbeknownst to many, a real rise awaits on a lonely hill on the edge of town, steeped in local legend

One of the only memorials dedicated to journalists who died in combat.

This Maryland farm is known for its amazing corn mazes and its 30-foot junkbots.

A pre-Industrial Age iron furnace and the site of a nearly-forgotten piece of Black history.

A Civil War Museum with some notable medical antiques.

This four-story steel sphere in Maryland was used to test biological weapons.

Situated in a bustling intersection, this "mobile" monument that honors local veterans from five different wars has moved several times but appears to have found its final resting place.

The fastest transatlantic ocean liner sat abandoned in a Philadelphia shipyard for decades.

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

Housing the National Women's Party since 1929, this historic house is now a monument to the fight for gender equality.

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

This unassuming passageway played a key role in one of the most important events in U.S. history.

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

America's Most Wanted's set resides in this tribute to the history of crime and punishment.