You will want to visit the Willis tower and the Navy Pier as well as the John Hancock Center and the Cloud Gate in Chicago. There are three major sports events fields and a great museum - the Field Museum of Natural History. This is only one of several museums in Chicago. The Polish museum and DuSable museum of African American history are well worth a visit. You should also go to the art gallery at the Art Institute of Chicago.
I wouldn't miss the Buckingham fountain, the planetarium or the aquarium. There are three theatres, and more art galleries such as the Museum of Contemporary Art, as well as other interesting buildings like the Auditorium and Water Tower Place. You won't be at a loss for things to do in Chicago.