It’s free, open to all ages, and a local tradition: an alfresco music mélange Thursday–Saturday on the Memorial Union’s outdoor terrace (800 Langdon St., 608/262-1331, www.union.wisc.edu [1]). The whole place really gets bopping Friday and Saturday—the music cranks up and the beer starts flowing. During inclement weather, the whole shebang moves indoors to the cavernous Rathskeller (an acoustic death zone).
You are supposed have a UW ID and valid driver’s license to buy beer here; they're strict about it.
Links:
[1] http://www.union.wisc.edu