Once forgotten and built over, this historic Black cemetery now houses a poignant memorial.

Railroad officials in the early 1900s sought to spare travelers the sight of Roman soldiers’ private parts.

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

The oldest continuously operating fish market in the United States.

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

They sort through millions of dollars worth of diplomatic gifts on behalf of the government.

Corn-inthian columns with a uniquely American take on neoclassical architecture.

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

This statue of the "father of television" stands prominently in the United States Capitol.

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

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

An ear-piercing buzzer calls lawmakers to a vote with a series of long and short rings to form coded messages.

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

There just so happens to be a court even higher than the U.S Supreme Court: a basketball court in the building itself.

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.

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

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

Daredevil repair workers can worm their way out the access hatch, loop ropes over the apex and rappel down the monument.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

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

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

A gift from Japan, 17th-century lantern stands among the cherry trees at D.C.'s Tidal Basin.

On the Fourth of July this area will transform into a Pompeii-like storm of falling embers and ash.

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