One extra day from Arles - No car, where to go?

Aix is a charming, pretty town, and if you get bored you can visit Marseilles or Casis.

But if you are in Arles, you have some pretty good options too, including Orange and Avignon (a straight shot by rail, you can visit either or both), Nimes (ditto, and easy trip), Stes. Maries de la Mere (in the Camargue, a bus ride) and of course Arles itself.

If you are willing to make a transfer, you can go to the Pont du Garde (on a bus between Nimes and Avignon), which is both wonderful and a great swim spot.

Really an embarrassment of riches! Have a great time.

As Adam said there are definitely a lot of options - Aix, Nimes, Avignon, Orange, and maybe even Les Baux as well although I heard the bus from Arles to Les Baux is no longer operating. It sounds like you probably have a good idea of what these cities are though and want to hear personal opinions about the cities to choose the general favorite. I haven't been to any of them yet, but from what I've read so far, I'd choose Aix since you sounded like you wanted a more laid-back day (maybe Avignon or Nimes for a busy sightseeing day). Aix is also a quick bus ride from the Marseille airport (Marseille airport is halfway between Marseille and Aix). But like I said, I've never actually been to Aix so it would be good to hear other people's opinions on whether Aix is worth visiting as well.

Thanks, all! I've decided I'll spend the day in either Avignon or Aix. Will one be less crowded than the other in August? If you have a distinct favorite, please let me know!