Going to Chicago

.....in a few weeks for business. Staying at a hotel on Michigan Ave in the middle of The Magnificent Mile so judging by some maps I've looked at I'm kind of right in the middle of a lot of entertainment, which is nice.

My question for you Chicago heads or boarders well schooled on the ins and outs of Chitown is what MUST I see/do as a first time visitor? Cool local bars, must see sightseeing/picture taking, etc. Getting there on a Monday and leaving Thursday. Thanks in advance!