I'm still recovering from a fall where I sprained one ankle and seriously bruised the other knee (I didn't break anything, but I'm lucky I didn't break anything), but I'm reaching the limit of feeling like I really really need at least a bit of exercise aside from gentle stretching. If I had access to a pool I'd be set, but no gentle caress of the water for me.

I usually walk a good bit just going about my day-to-day, but I'm not up to that yet. What can I do to exercise that doesn't require knees that bend or ankles that can hold much weight for very long at all?