What to do or see in Chicago for half day?

Ill be attending business in Chicago, arriving around 7 pm into O'hare, the next day I will be free afternoon, and the 3rd day flying back at around noon. I would like to get advices of what to do or see in such short time, any MUST-GO restaurant ?, any advice for cool lodging in downtown.? I am doing business at Hoffman Estates, is it extremely far from downtown Chicago? Thanks