What to do in Chicago?

I’ll be in Chicago for 2 -3 weeks for work next month and am looking for things to do. I don’t think I’ll have much issue as I love cities and architecture so that alone should keep me occupied. However I understand there are a lot of sweet museums and such I should check out, so I’m looking for some more ideas.

I’ll be staying downtown, most likely near one of the JP Morgan Chase buildings, as that’s where I’ll be working. I have no problem hopping on a train and going somewhere. I don’t think I’ll rent a car though, too much of a hassle.