A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.

"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!”

Before Metro, Washington had a robust streetcar network—and you see the remains of this infrastructure if you know where to look.

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

A historic arena where the Beatles played their first concert in the U.S.

A diminutive memorial marks the site of a successful assassination by a right-wing death squad in America's capital.

This leafy estate is worth $18 million and is so grand it has two mailing addresses.

A much-maligned monument to teetotalism.

A computer bug so primitive it was an actual insect.

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

A heroic pigeon that, through a barrage of gunfire, delivered a message that saved over 100 lives in World War I.

An unassuming, powerful monument north of the U.S. Capitol bears witness to the resilience of Japanese Americans during a time of grave injustice.

A small triangle of DC grass is the final resting place of one of Sonny and Cher's songs.

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

Daily lunch spot for many of Washington, D.C.'s cab drivers.

Housing the National Women's Party since 1929, this historic house is now a monument to the fight for gender equality.

Four bald cypress trees in Lafayette Square, across from the White House, mark the southern edge of a 100,000 year old cypress swamp.

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

The privately owned cemetery that holds room for Washington's finest when they step down from life.

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

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

A super-sized promotional trick that is now a D.C. landmark.

A traveling postal dog covered 48 states and more than 140,000 miles, and he lives on as taxidermy, patched up with a rabbit's foot and a pig's ear.

The first purpose-built art gallery in the United States is once again open as a center of craft arts.