Chicago is a very easy city to get around in. There's plenty to do within walking distance of the Sheraton and lots more only a short cab ride away, even if you don't feel adventurous enough on this trip to try the CTA. Why don't you tell us a little more about what you're looking for. Quiet? Romantic? Interesting? More or less expensive (feel free to give us a dollar range). Any particular ethnic food you'd like to try?
Where are you going to be between breakfast and lunch? Shopping the mag mile? Strolling Millenium Park? In meetings at the hotel? Any more info will help us help you.