Architecture in Washington, D.C.

This nine-story building is the oldest standing skyscraper in D.C.

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

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

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

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

There’s a special club house at the top for the bell ringers.

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

There's an old indoor swimming pool hidden directly underneath the White House Press Briefing Room.

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

The grand marble structure next to the White House is Andrew Carnegie's temple to Pan-American diplomacy.

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

A wondrous old library overlooking the nation's capital.

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

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

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