A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

Lines from a walking song are etched into a rock in Natural Bridge State Park.

After his presidency, George Washington planned to live only a few blocks from the Capitol building.

The tunnel under the Capitol Building where Congress takes out its trash.

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

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

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

Home to items never before seen by the public.

A lawn full of retired spacecraft on display at one of NASA's first research labs.

A relic of FDR's brief foray into utopian urban planning.

The oldest continuously operating fish market in the United States.

A historic arena where the Beatles played their first concert in the U.S.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

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

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

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

An overlooked memorial honoring the local Washington residents who died in World War I.

This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

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

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

Nearly 200 prehistoric giants lurk among the trees at this theme park.

Manatees congregate around a power plant's discharge canal where the water is especially warm.

These former theme park figures have a new lease on life outside a water plant-turned-restaurant.