Floating above official Washington, the dome of the United States Capitol is one of the world's most recognized landmarks.

The contemporary Capitol actually has two domes, though, one inside the other. The outer dome, on top of which sits Thomas Crawford's bronze sculpture ''Freedom,'' was completed during the Civil War. The second, inner dome was finished in 1866, when scaffolding was removed from below Constantino Brumidi's fresco, ''The Apotheosis of George Washington,'' 180 feet above the Rotunda floor.

It is 365 steps from the Capitol basement to the top of the outer dome, a steep climb up a narrow metal staircase that snakes between the double dome, out of sight to visitors below, to an outdoor walkway.

A behind-the-scenes tour offers a visitor a rare peek at a 19th-century engineering marvel -- iron trusses supporting the cast-iron outer dome -- and breathtaking (and, for some, dizzying) views from high above the Rotunda and atop the outer dome overlooking the nation's capital.