tontybear wrote:The architecture foundation has some fantastic walking tours with access to buildings the public dont normally get into.
http://caf.architecture.org/Page.aspx?pid=698
Spot on - and their River Cruise is also wonderful, as it offers views of the great buildings from perspectives you would otherwise not be able to access. TBH, you could easily consume 4 days just doing architecture-related tours. CAF do a "Bike the Lakefront" tour that's a lot of fun if you like that sort of thing, and for something definitely off the beaten path I'd take a ride to Hyde Park, check out the U of C campus and the Robie House.
This gal is doing all the CAF tours in a year (there's 85 of them!):
http://www.85tours.com/It's a useful blog for what you can expect to see in several of the tours, since you won't have a lot of time there it might help you figure out which tour would be best. I'd still probably pick the river trip over anything. I did it 15 years ago the first time, and loved the place ever since. Oh, s@d it, we're going back next year

If you have even the slightest interest in sports, go spend an afternoon at Wrigley Field - great place. Ask the locals at the game about Billy Goat, then go grab a drink at the bar as pjh suggests.