Take a look at their Natural Cultural Health Service.
I could have spent the whole weekend there: in the park, the gardens, the cafe, the galleries, the shop. Free, family friendly, well-used on a sunny Saturday - well done my old University of Manchester! I liked to go to the Whitworth when I was studying but it was darkish, and old fashioned with a played out park outside and very few people inside and the cafe consisted of two tiny tables in the entrance way.