The walls of the iconic dome are hollow and have a secret stairway.

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

A secret greenspace hides atop a Capitol parking garage.

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

The most accurate timepiece in the world.

A painfully obvious spy house sits right across the street from the Russian Embassy.

A muscular Art Deco monument represents the struggle between regulators and unbridled markets.

A much-maligned monument to teetotalism.

When it comes to handsignals (and colonialism) rock always beats scissors.

The sculptor was instructed to add “stallion attributes” to the general's bronze mare.

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

The National Park Service’s best-kept secret with views that rival any in D.C.

A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.

Home to items never before seen by the public.

The hippo that stands on this university campus was once a drunken flea market purchase.

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

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

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

The controversial urban planner who designed Washington, D.C., was buried in Maryland, and can presently be found in Virginia.

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

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

The innocent intentions of this monument are somewhat lost in the sculpture's muscled imagery.

A lightship turned museum, outfitted with artifacts from the vessel's past as part of the U.S. Lighthouse Service.

This cannonball stands as a reminder of the final act of a fleeting governor amidst a revolution.