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.

The early data processor factory founded in Washington for the 1890 U.S. Census went on to become IBM.

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.

The only National Monument ever to go missing for nearly 50 years then resurface in a dump.

Before Nixon, "watergate" meant canals.

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

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

A building shaped like the Army Corps of Engineers logo, because why not?

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

Decades before the scandal, this staircase on the river was a literal "water gate."

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

The house where John Wilkes Booth conspired with his co-conspirators.

The oldest continuously operating fish market in the United States.

The national park was once a plantation estate.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

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

The oldest existing one-room brick schoolhouse in Loudoun County.

The Aldie Gristmill was once the largest factory of its kind in Loudoun County.

The only surviving 19th-century water-powered mill found in the Washington, D.C. area.

These unusual rooms on wheels are holdovers from the 1960s.

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