What fun cheap or free stuff do you like to do?

I am curious as to what fun cheap or free things you do for entertainment with the family.

We love the library.  The storytimes and special programs they put on are AWESOME - and most are free!

Though not initially cheap up front, we have a zoo membership and a children's museum membership this year.  We use some of the money that we get for birthdays and Christmas to purchase two memberships each year.  I usually try to do one outdoor and one indoor to get a nice variety.  Then when we have days when we think we have nothing to do, we can always take advantage of one of the memberships and spend nothing out of pocket.  I do this instead of going to all of the kid places that are around town and spending about $15 each time!  We use the memberships at least once per month so they more than pay for themselves.

Once the nicer weather arrives, we love to go to all of the parks Colorado has to offer.  We also love the summer concerts in the parks that lots of cities are now putting on.

So my question for you is what do you do for cheap or free fun?  Leave a comment to let others in on your secrets!