George,
There are many fine things to do in Chicago. Do you know where you'll be staying? Do you have particular areas of interest? Architecture, food, theater, nerd junk, etc? I think Downtown Sound has started at that point, which means there should be a free concert in Millenium Park that Monday. It might be worth checking out who is playing, as those are always a fun time(and free!). The Chicago Cultural Center is pretty neat(located downtown near Millenium Park) and usually has interesting art things happening there. If you're going to go to a museum, I would make it the Field, but I am a sucker for the history of that place. The taxidermy there is wonderful. Everytime I go I notice something new. Also, lots of dinosaurs if you're into that.
FOODWISE: west loop has lots of incredible incredible options that are both fancy and affordable. the publican, nella coate, girl and the goat, little goat, au cheval, etc etc. blackbird is around there as well, and all of the afore-mentioned restuarants hover in the 14 - 20 range, and all are fantastic. if you're looking for regional treats, a chicago-style hot dog is perhaps the most perfect food known to mankind. deep dish pizza is an abomination suitable only for greenhorns, but the chicago-style hot dog is wonderment in a bun. where the best one lives, whatever, who cares, it's akin to pizza or americanized chinese food, even a bad one is pretty great. some people will tell you that the wiener circle is the place to go, but that is incorrect. if you can get to hot doug's, and don't mind waiting in line for awhile, hot doug's is filled with sausage/hot dog joy. their chicago-style is good, but their specialty sausages are really really wonderful. their hours are weird and they might be closed that week, so double check that if you're interested.
NERD STUFF: honestly, I'm bad at this. i hear really great things about analog the bookstore, but i've never been. wanderer's refuge is a great gaming store, but i imagine you have those in seattle. challenger's is a fantastic comic book store, but again, i imagine you have those in seattle. there is a lovely sci-fi/fantasy book store in my neck of the woods called bucket o' blood. it's run by a fellow who used to own a chicago punk label, and it's very well curated. also well priced, which is honestly a rarity in chicago, IMO.
OTHER THINGS: if you get a chance, try to take in a show at the neo-futuriaium. this is an incorrect spelling, but I am writing this in haste. it is the home of "too much light makes the baby go blind" and various other interesting theaterical experiments. they're one of my favorite groups in chicago. AFTERWARDS OR BEFORE, you can grab ice cream at george's! which is wonderful. again, i'm not sure of their scheduling, but you have the internet. you can investigate. if you're into country music at all, you could do much worse than to check out robbie fulk's residency at the hideout on mondays. it's a $10 donation, and he plays a lot of classic 50's and earlier style country usually, depending on who his guest is that night. if you're into film, there's the gene siskel film center downtown, the music box theater on southport, or facets on fullerton. all generally have something worth your eyeball time going on. siskel is usually a little bit more high-brow, while facets and the music box are into the weird and off the wall a bit more.
um. yeah. chicago is great! i don't think i have any plans for those nights you're here, though i might also be out of town on business, depending. but if i'm around and you want a guide or someone to traverse the wilds of the chicago transit authority with, let me know. we could also try to round up some of the other chicago IF folks depending on their schedules.
let me know if you have any questions, or want more specifics.
ed.