ICA Museum is a great way to spend a day checking out alternative, progressive artists (if you've had enough of renaissance paintings at the MFA). They have awesome displays and touring exhibitions from people like Anish Kapoor (the Bean in Chicago), etc. If it's nice out, you can take a walk around the harbor afterwards or go to one of the many new restaurants in the Waterfront neighborhood. Pick a pretty day with great Fall weather and take a trip to the ICA Museum!