chaosrob hit some really good ones, especially the modern art museum. I used to take the water taxi across town sometimes; while it’s nothing special really, it’s fun if you’ve never done it before.
One place I think is fun for tourists that he didn’t mention is Jilly’s.. it’s kind of a Chicago institution.
Some additional suggestions:
1. Have drinks or dinner at the Signature Room on the 95th floor of the Hancock building – amazing view. (chaosrob referred to the Hancock viewing deck, which is one floor up; I prefer the bar itself though.)
2. Walk or bike around the Wicker Park area and check out the shops & bars.
3. The Matchbox is a tiny little bar that it can be fun to cram into. It really is tiny, and therefore.. intimate. :)
4. If you’re staying in a downtown hotel, ask your concierge for nightlife suggestions; if he’s any good, he’ll be able to point you to places downtown that will match your interests. Downtown Chicago has a ridiculous number of restaurants & clubs, from moody piano bars to ultra-hip dance clubs, and everything in between.
If you get steered to Division street, just know that the drinking is heavy & a bit wild in that area; maybe that’s what you want, or maybe not. :)