there are many lovely and beautiful parts on french routes.
- a week on via podiensis starting in le puy will get you into the valley of the lot river, perhaps even as far as estaing. you cross the spectacular aubrac plateau and visit some lovely historic towns. there is a daily pilgrim/hiker mini van transport to and from le puy as far as conques. you need to arrange the transport in advance (they also do backpack transport). it is advisable to book accommodation a day in advance on this part, because the stretch from le puy to conques is the most popular.
- a week on the beautiful célé variant of via podiensis from figeac to cahors. don't miss the pech merle cave paintings (reserve well in advance), chemin du halage and st cirq-lapopie. trains at both ends, and in between a sncf bus. reservations very advisable, as there is roughly one gite per town and it's not very big.
- on via tolosana perhaps the part between montpellier and castres that includes a big town, a beautiful gorge, a devil's bridge, two abbeys, and lots of hills. there is accommodation every day but the capacities were pretty small when I was there in 2009, so call ahead. both on the train line.
- perhaps a section on voie du piemont pyrenees between carcasonne and saint-lizier or saint-larry. I dont' know the first part, but later you walk through the amazing cavern of mas d'azil, sleep in an original pilgrim hospice, and can visit several frescoes of st jacques. this requires calling ahead to alert people you are coming. carcasonne is on the train line, but getting back requires a research for buses.
- and, even it's not a camino, a part of spectacular sentier cathare? I would recommend starting in tuchan or padern and going as far as a week takes you. reservations are recommended. and this definitely requires a research for buses. if you are interested, I can give more detailed info (from 2012).