Tips for staying active?

Any suggestions on how to stay active in the last month and a half of pregnancy? I live in the Midwest and it's been continuously 90 degrees with 50% humidity and I've been miserable. I typically do all sorts of outdoor activities all summer so I'm at a loss as to what to do since it's too hot to go hiking or walking outdoors. My ankles have been so swollen and my hips hurt so bad I just don't feel like doing anything but I know I need to stay active.