Almost every fitness club allows a free week trial for walk-ins. Just try walking into an LA Fitness or Lifetime and tell them you want to try working out for the day and you will probably join if you enjoy your experience. They will put you through a quick meeting with someone working there, but it only last about 10 min. Come with a friend and enjoy a quick workout, some basketball, and a sauna. Be aware, this will only work once every 6 months or so, but you can go to different clubs in the meantime.
Cheap and fun things to do around Minneapolis/St.Paul