Paris to Barcelona stopover city?

Because they are on the rail line from Paris to Barcelona, the logical choices are Avignon, Nimes, or Montpellier.

A few years ago I took direct train from Paris to Nice, spent about 4 nights there, and then took a train to Barcelona.
I enjoyed all three locations very much. The train trips were a bit long, but I prefer trains to flights when it's feasible, and they were relaxing.

Tocard's recommendations are good! Towns/cities like Nimes are close to other cities that can be done in day trips by train.

Expanding on the suggestions above, Avignon would be my suggestion. Nice is a truly fantastic city, where I’ve spent more time in the past 5 years than any European location, although with what you’re describing, I’d recommend Avignon, and spend 4 days. Use 1 to make a side trip to Nimes, and another to see Arles for the day.

Enjoy your midway stop, and Barcelona, too!

I guess that Toulouse would be too close to the Barcelona end. Different though, and a lot different to Barcelona.

there is a high speed rail between Paris and Barcelona. I don't think it goes close to Provence.

https://www.thetrainline.com/en/train-times/paris-to-barcelona

Provence is that area of France between the Rhône River and the Italian border. Avignon is on the eastern bank of the Rhône River and in Provence (PACA). Nîmes and Montpeller are in Languedoc or the area on the west side of the Rhône River.

Depending upon the scheduling, Paris to Barcelona trains could stop at any of these locations.

Stopping in the Provence area would be a fun sidetrip and I would recommend 3-4 days at least. You could base in Avignon and then day trip throughout the area. There is much more to see than just 1-2 nights. We really liked Arles, but the TGV goes to Avignon and you would have to rent a car to get to Arles as a base camp city.

All the stops on the SNCF-RENFE Paris-Barcelona train route -- https://www.thetrainline.com/en/train-companies/renfe-sncf

I lived the summer in Nîmes 4 years ago, and would highly recommend Nîmes as home base. Not only is the town beautiful/festive/friendly, it has high quality Roman ruins, beautiful parks, lots of good lodging/dining options, wonderful indoor and outdoor food markets, an easily walk-able town full of shady tree-lined streets, and lots of festivities in summer months (dancing+concerts+outdoor markets one evening every week in July). Best of all, Nîmes is the regional bus hub with cheap and convenient daily buses to Avignon (Avignon festival in July), Pont du Gard, Arles (the big Saturday weekly market), Uzes (Fête Votive in August) -- all well under 1 hour of scenic ride.

40 min on cheap TER train from Nîmes is Aigues-Mortes, a lovely well-preserved walled medieval town -- their famous Fête de la Saint Louis in August is spectacular fun, even the visitors come in medieval costumes.

Regional bus system map + TER:
https://www.edgard-transport.fr/presentation/?rub_code=1035

Between Nîmes and Barcelona is the impressive walled medieval town Carcasonne (Festival in July). Train station to the old medieval town is walking distance. Carcasonne is an easy day trip from Nîmes on SNCF IC/TGV (under 2 hr ride). You can also go from Nîmes to Carcasonne for a day and connect to SNCF-RENFE Barcelona-bound train at Perpignan, a short TER ride from Carcarssone.

FYI -- every year, Avignon lodging price skyrockets before-during-after Avignon Festival, according to my acquaintance who makes 300%+ profit every July from his family's 4 rental properties in Avignon.

Wow, thank you so much for all the replies. Nimes does look like a great place to go with the little research I did and with all of your suggestions. I do like that there are short day trips from there as well. For now that looks like the leading city!

Avignon has high tourist impact which drives the accommodation and other hospitality prices up as noted by other posters for higher post-covid price forecasts. Directly on the train line, an overnight stop could allow for catching the highlights. I also liked Aix-en-Provence for a stop over, it is busier, but could be the center of a lot of day trips in Mediterranean Provence and it is easily reached by commuter train from Marseille. Nimes does seem like an easier stop over if you are going to Barcelona.

IMO Ashley's recommendation of Nimes as a home-base is a good one.

We love Collioure on the French Mediterranean
coast north of Barcelona and would happily return there for a week or more. . It has art history, a castle, charm and a beautiful waterfront. I assume there is train service nearby but we had a car. It is much more than halfway though.

There is regional-train service to Collioure.