Como Zoo is a great free attraction! For a free zoo, they really outdo themselves, with giraffes, tons of gorillas, polar bears, and a myriad of large cats. The zoo isn't too large, and the layout is quite sensible, so it is good for small children and big kids. Parking is free as well, so that just adds to the benefits.
If you're done with the zoo and conservatory, take a walk around the 1.5-mile lake, barbeque by the fire pits, take 9 or 18 holes at the golf course, or take a dip in the pool. In winter, they turn the golf area into a ski hill/sledding area where they offer lessons.