Paris to San Sebastien via where?

I am travelling from Paris to San Sebastien and would like to stop off at one destination on my way through. I am thinking Bordeaux but don't know a great deal about this region of France. I am backpacking and will be relying on trains for transport, so driving is not an option. Can Bordeaux still be enjoyed without a car?

Also, how difficult will it be to travel from Bordeaux to San Sebastien?

There are several places you can visit in between Paris and San Sebastian. If you are looking for major cities I would recommend you Tours and La Rochelle, apart from Bordeaux that you have already mentioned...

Then, souther to Bordeaux you have Biarritz & Bayonne, two beautiful cities one very close to the other...
You can take the TGV from Bordeaux to Hendaye (stops in Biarritz as well). And from Henday, look into the train linking the main railway station (Gare in French) with Irún (spanish border) and finally San Sebastian.

If you have any doubts or want something more specific, send me a message!!!