This bridge over D.C.'s Rock Creek Park is sometimes called the "Buffalo Bridge" because of its four buffalo sculptures, which were cast from a single piece of bronze.

The final resting place of an unidentified revolutionary soldier sits behind a Virginia church.

The graveyard holding the remains of George Washington's slaves was forgotten for nearly 200 years.

This brick-lined pedestrian walkway was once a railway tunnel used during the Civil War.

This stately building in Alexandria, Virginia was built by Freemasons to honor one of their most famous members.

The narrowest house in America is seven feet of pure spite.

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

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

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

Once a sewer culvert, this road tunnel now offers cyclists and pedestrians a subterranean stroll under the C&O Canal.

The grand marble structure next to the White House is Andrew Carnegie's temple to Pan-American diplomacy.

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

Look closely and you’ll notice that the color changes a third of the way up the tower.

A gorgeous mural outside a beloved D.C. restaurant pays homage to famous Black Americans.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

A historic ruin just 20 feet away from a busy highway onramp.

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

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

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

The most decorated dog of World War I is preserved in the Smithsonian.

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

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

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