Dominating the Chicago skyline for 40 years is the Willis Tower, known as the Sears Tower until naming rights were sold in 2009.    A 108-story 1,451 foot tall skyscraper, it was the tallest building in the world when completed in 1973 and held that title for 25 years.   From the 103rd floor observation deck,  Indiana, Illinois, Michigan, and Wisconsin can be viewed on a clear day.   Interestingly, the design of the tower was inspired by a pack of cigarettes of differing heights.