What Is the Largest Office Building in the World?

The Pentagon, which is the headquarters of the United States government's Department of Defense, has been the world's largest office building since it opened on January 15, 1943. It lies on the west bank of the Potomac River in Arlington, Virginia, just across from Washington, D.C.

The Pentagon was named for its shape, which means a five-sided figure. It has five rings, one inside the other, with corridors going from the inside out, like the spokes on a bicycle wheel. Each outer ring is 921 feet long.

To walk through all its rings and corridors, from the basement to its fifth floor, you'd cover 171/2 miles. About 29,000 people, both civilians and military personnel, work inside this $83,000,000 building, including those who have to clean its 7,748 windows.

The Pentagon also has the world's largest telephone system, with 45,000 phones handling 280,000 calls every day!