I wouldn't say the south of France is your best spot for a week of "hiking and swimming" with some culture. For beaches and hiking, maybe Antibes or Nice. Or, The Camargue. We skipped it, but it does have beaches, kayaking and hiking and nature, and, I'm told, big mosquitos. With only one week in Provence, for us, Avignon was best for history, culture, cities, and to a lesser degree, countryside forays. In Avignon, you're within an easy day trip to Arles, Marseille, Ile-sur-la-Sorgue, Nimes, Uzes, Pont du Gard (although I'd recommend a car for this one. The bus is a bit awkward.) We stayed inside the wall at an Airbnb near Les Halles. Only a 10 minute walk to the train station, easy walk to the town's highlights and lots of good restaurants. We spent a week each in three base cities/towns: Nice, Roussillon and Avignon. Roussillon is a bit isolated unless you have a car, and even then it's still not easy unless you want to do all the hill towns and not much more. OTOH, it's good for being off the beaten track and relaxing. I found Nice little more than a big city, but with a beach. Day trips are nice, though. Depends what you want to do most. With only a week, you can't have it all. Life will be easier in September rather than August and certainly still warm enough to enjoy everything outside.