Museums are a great way to spend time learning and having fun on your own, with family, and with friends. I've been checking into the various museums in Wisconsin to find some places to visit when I get a bit of time to do so. I was nigh overwhelmed by the number of them listed on Wikipedia here.
Also, on tripadvisor.com, they have a more manageable list here.
Finally, on travelwisconsin.com, they have a more eclectic list here.