We are beginning the first 4 days on the Cote D'Azur and plan to do an overnight in Carcassone. We have another 4 days or so and here's the dilemma. Do we go north to Annecy, Laussanne, Montreux and Gruyeres in Switzerland or to northern Spain and to Barcelona? We are going in early Sept. and renting a car and are fine with driving distances in Europe. Our interests are art, history, hiking, photography, sightseeing etc. We enjoy both cities and small towns and this will be our 5th european trip. Thanks all!
As a fan of Carcassonne, I'd say, skip Carcassonne, which must be a good 4 to 5 hours west of Nice, and just head north as you describe. Beware of big drop-off charges if you return the car in a different country than the one in which you rented. Switzerland also requires a vignette.
Personally I would spend the rest of the time a short distance from the Cote d'Azur in western Provence. The Luberon, Arles, the Camargue, Aigues Mortes, Pont du Gard, etc. tick all your boxes.