Sun - how about
just sit down and stretch your arms? It's tiny, but it might help keep you in the exercise groove while your knee heals. Is there a pool you can swim at? That's HUGE exercise and shouldn't hurt your knee. If you're really ambitious, you could get a 1 or 2 lb dumbbell and do some ar weightlifting.
Even sitting and knitting keeps you more active than sitting and doing nothing at all.