We need some advice for this drive: best route to take , and where to overnight in France along the way.
Does your trip end in France, or will you be looping back into Spain. Renting a car in Spain and returning it in France will probably involve a very large international drop charge.
We will eventually be returning to Barcelona
There are quite a few terrific towns between those two places, worth some detouring, if necessary. Albi and Cordes-sur-Ciel pop into mind.
I did exactly this journey in 2012. Here's how I did it.
Train from Barcelona to Perpignan, France. The advantage of crossing the border before renting a car is dropoffs are free within country, but prohibitively expensive cross-border.
Rented a car in Perpignan and drove to Carcassonne. Carcassonne is not to be missed: the best preserved medieval walled city I've ever seen. A daytrip there would be horrible, with all the bus tours, but to stay in the walled Cité overnight is magical.
Drive from Carcassonne to Beynac in the Dordogne, via Toulouse and with a stop at St-Cirq-Lapopie, reputed to be "Le Plus Beau Village du France."
As you are returning to Barcelona, you could do the whole thing as a drive, instead of train to Perpignan. I would recommend the same route though.
I am in the early planning stages of doing the exact same trip in September 2020.
One big question--how much time do you have?
We have 3 1/2 or 4 weeks (still working on figuring out exactly how much time the Significant Other can take off), and are planning to take about 8 days lazily driving up from Barcelona to Sarlat, staying in Sarlat for 4 days, and then spending the rest of the time heading back down the Atlantic coast, ending with 2 days in Saragosa, and 4 (including the departure day) in Barcelona.
We had the pleasure of visiting Saint-Cirq-Lapopie, Domme, La Roque Gageac, and Cahors recently. All four cities were beautiful and interesting. If you go to Saint-Cirq-Lapopie, the walk along the river to the town is really beautiful, along and under cliffs, through farmland, and then up a steep (but short) incline to get to the town. I think there's often a boat option, but we walked. It was peaceful and lovely.
Laurie
We did this trip several months ago. Picked up a leased car at BCN, headed for two nights in Carcassonne (Europe's largest medivial castle), and stayed in Sarlat for 6 nights. Sarlat is an ideal central location for many of the sights in Rick's book. On the way back to BCN a stop in Girona is a must if you like medieval core cities. Stay in or near the core area. Game of Thrones did a lot of shooting at this location. Finally, if you have any interest in Dali (I had no interest), head to his top-notch and interesting museum in Figueres and his home in Cadaques. You will not be disappointed.