If you want to be in some A/C, Smithsonian Magazine Museum Day is on Saturday. That means that besides the already free Smithsonian, there are other museums for the having. Go to the website and print your free tickets.
If you want some history, there are all kinds of walking tours. It is What’s Out There Weekend, in which, supposedly, all of Washington collectively wakes up to the fact that there is a lot of stuff to go do. Whoa, Nancy, do you realize what I just discovered? We have options! There’s all kinds of stuff–there’s the Tregaron Estate in Cleveland Park, tours in Adams Morgan, and MORE! I’m so glad we didn’t go to Michigan to visit your mother.