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

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.

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

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.

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

This forgotten boat elevator was an engineering marvel in its heyday.

This massive swimming pool is the high tech home to the human-powered submarine races.

This church built atop a gas station promises to "equip you for the next stage in your life’s journey."

At 207 feet, one of the world's longest continuous escalators.

The controversial urban planner who designed Washington, D.C., was buried in Maryland, and can presently be found in Virginia.

This lovely picnic spot featuring thunderous jet landings is an aircraft spotter’s dream.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

This small pedestal marks the spot of the first lot of land sold in Alexandria, Virginia in 1749.

Long buried under the 20th-century landscape, this lift lock of the Alexandria Canal is the lone remnant of an ambitious early American transportation project.

The narrowest house in America is seven feet of pure spite.

A former major munitions plant that has been converted into a sprawling art space.

This brick-lined pedestrian walkway was once a railway tunnel used during the Civil War.

This rare triple-jurisdiction drawbridge passes through Virginia, Maryland, and Washington, D.C.

America's first federal monument.

Located at the former Lorton Prison the Lucy Burns Museum tells the story of the 91 year history of the prison including the dark chapter of its involvement in the women's suffrage movement.

This little brick tunnel built by Confederate forces was used to conduct surprise attacks on the railroad.

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

At Washington's Dulles Airport is a satellite museum (no pun intended) with three quarters of a million square feet of aircraft history.