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

A much-maligned monument to teetotalism.

The institution is sitting on a goldmine of 21,000 paints, varnishes, pigments, and primers preserved for posterity.

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

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

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.

"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.

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

The oldest continuously operating fish market in the United States.

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

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

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

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

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

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

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

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

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

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

‘Bush the old fire dog died of poison July 5th, 1869. RIP.’

A historic ruin just 20 feet away from a busy highway onramp.

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.