A secret greenspace hides atop a Capitol parking garage.

This statue of one of baseball’s greatest pitchers looks like something out of a sci-fi horror movie.

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.

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

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

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

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

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

Art deco landmark on the outskirts of Washington, D.C.

Members of Congress have traveled between the buildings on Capitol Hill for a century hidden from tourists, press, and storm clouds.

A little marble compass above George Washington's (empty) tomb in the Capitol marks where D.C.'s four quadrants intersect.

The only Civil War battle in Washington D.C. took place near this highest natural point in the city.

A celebrity from the late Cretaceous period.

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

The most accurate timepiece in the world.

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

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

The national park was once a plantation estate.

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

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

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

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

Home to items never before seen by the public.