Willis Tower
Willis Tower is a 108-story, 1,451-foot skyscraper located in Chicago, Illinois. At the time of when it was completed in 1973, it was the tallest building in the world. The World Trade Center, located in New York, recently took it's place as the tallest building in the world. It is also commonly known as Sears Tower. The Willis Tower weighs about 222,500 tons.