Fodor's Expert Review Aon Center
With the open space of Millennium Park at its doorstep, the Aon Center really stands out. Originally built as the Standard Oil Building, the 83-story skyscraper (first referred to as Big Stan) has changed names and appearances twice. Not long after the building went up in 1972, its marble cladding came crashing down, and the whole thing was resheathed in granite. The vertically striped structure sits on a handsome (if rather sterile) plaza, where Harry Bertoia's wind-chime sculpture in the reflecting pool makes interesting sounds when a breeze blows.