Nice to Perpignan-6 days to kill?

If you don't expect to be back in that area again with a car, I'd tend to focus on places for which a car is required. I'm currently researching my own car-less trip to France, and I can tell you that the Gorge du Verdon sounds as if it will be tricky for me. I certainly won't be able to see both sides of the gorge and stop at will. I believe Les Baux has no public transportation, and the marshy Camargue area south of Arles at the mouth of the Rhone is best with your own wheels. The Cathar sites west of Perpignan are other destinations I'm going to miss.

I'm sure others can provide a lot more ideas, since I'm just coming up with places on my "I-can't-get-there" list.

I enjoyed Cassis (not far from Aix). Also the Camargue was interesting. Slightly past Perpignan the beach town of Collioure is very enjoyable.

If you return your car at the train station in Perpignan be aware that you have to drive into a poorly marked entrance at the station.

Oh gosh, where to begin! There is so much between Nice and Perpignan...I'm more familiar with the western end of your route.
- Montpellier, Pezenas, Beziers, Narbonne, Coulioure are my favorite towns...not necessarily in that order.
- The Abbaye de Valmagne winery outside Pezenas is unique and beautiful.
- The cathedral in Narbonne was only partially finished but is still quite spectacular. Pretty town also.
- Beziers - the cathedral there is also worth a stop...it is on a hill overlooking the town and the river far below...climb to the top and enjoy the view.
- Pezenas - it's just a very nice tiny town with winding, cobbled streets and amazing shops. The town gives breaks to artists and artisans so they can rent commercial space to sell their creations. Fantastic weekly market here as well.
- There is a small museum of antiquities that have been pulled out of the sea in Agde. Musee l'Ephebe...it's really interesting if you're into such things.
- Montpellier is a smallish city with a beautiful city center and pedestrian area...it's very French and well worth your time.
- Coulioure is a seaside village worth visiting not too far from Perpignan...there is a beautiful promenade wrapped around the small bay...a lovely tower at one end and a castle overlooking the other end. Great cafes and shops right along the water...the impressionist and fauvre painters hung out here back in the day and it's easy to see why when you go there.
- Take a small detour and venture up into the Cevennes...visit the pilgrimage town of St. Giullaume le Desert and the river gorges leading up to it. There are many caverns in that area that can be toured as well.
- The area around Pezenas, Beziers, and the Cevennes is dotted with "village circulade", small villages built in a circular pattern to provide defense back in the days when this was a necessity! Pezenas is one of the larger ones.
- You'll drive near the Camargue with its wild horses and flamingoes as well...I haven't had a chance to get down to see that but you can easily make the time.
- The Canal du Midi criss-crosses your route...it's especially lovely running out of the town of Agde towards the west.
- You can go see traditional water-jousting in hard to describe boats down in the town of Sete.
Your route is a great one and there is plenty to see! Hope this gives you a few ideas!

Day
1. Nice to Aix-en-Provence (2 nights) by train
2. Day to Marseille by train
3. Pick up rental car and drive to location near L'Isle-sur-la-Sorgue (3 nights)
4. Avignon, Saint Remy
5. Arles, Les Baux
6. Drop car in Avignon and then by train to Barcelona

So many locations in Provence - you can't really go wrong.