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

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.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

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

Home to items never before seen by the public.

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

Before Nixon, "watergate" meant canals.

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

A portal into the bricked up canal that runs through the heart of Washington D.C.

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

The "lovely red Vega" of the legendary record-settling pilot.

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.

This lovely pocket park is one of the most under appreciated in D.C.

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

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

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

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

The romance of early commercial flight still fills this Art Deco destination.

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

Right next to departures—how convenient!

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

The national park was once a plantation estate.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.