The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

The iconic D.C. restaurant where the Cuban Missile Crisis was negotiated, now a Walgreens.

It was once the base for a series of domestic terror attacks.

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

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."

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.

A hidden passageway now marks the site of an assassination attempt on Ronald Reagan that some say broke a 140-year-old curse.

The first memorial dedicated solely to the Black troops who fought for the Union.

The school tested mustard gas for the U.S. Army during World War I.

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

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

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

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

A much-maligned monument to teetotalism.

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

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

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

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

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

The most accurate timepiece in the world.

Perhaps the most scandalous statue of America's first president.

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.