...LIBRARIES.
We go to the library at least once a week at the moment. Most weeks it's twice, sometimes more!
When I was on maternity leave Kit and I went to the library pretty much every other day, and I think it kept me sane as a constructive way to get out of the house while not spending any money. All the local libraries had a session of 'Bounce and Rhyme' for babies and toddlers, and they were all on different days - we library hopped!
Now I'm working part-time, we only have two days of the week to play with where there are activities to participate in the library fun (they don't have activities on a Saturday - but we sometimes go then too just for the books, and they are closed Sundays sadly - but I guess books need a break too!).