Basque Country of Spain and France

TGV from Paris to Bordeaux and then train to Biarritz.

Look at flying Aerlingus to Dublin and then RyanAir or Easyjet to Biarritz. Unfortunately you may need to get to Chicago, JFK or Boston to get on Aerlingus.

I'll make an assumption you are asking about arriving to begin the Basque Country Tour.

My choice was flying from the USA West Coast to Paris CDG, an airport bus to Montparnasse Station (Gare), and a TGV train to Bayonne. Nice to relax with a sandwich and a bottle of wine bought before boarding the train. Total time might be CDG to Bayonne should be about 7 hours, but TGV is nicer than waiting around an airport. Other tour members did fly into Biarritz, via a couple connections, then you must take a short bus ride into Bayonne. No train to or from Biarritz airport.
Train from Madrid to Bayonne takes a few changes and might take a lot longer.

Likewise….I am all for simplicity. I flew into Paris. Took a short flight to Bordeaux. Took a city bus to the train station across town. I caught the bus outside the Bordeaux terminal (not a big place). Got a short "drive-by" bus tour of Bordeaux. Bought my train ticket to Bayonne and "trained" into Bayonne. It was a wee bit more convoluted than I would have preferred……but it was the cheapest….by a lot.

I had to change terminals in Paris…..but not airports. The train station experience in Bordeaux was a little stressful, but I kept asking questions until I was 87% sure I was getting on the right train. The people there were most helpful.

FYI…..it was NOT a TGV from Bordeaux to Bayonne. And…..just took a taxi from Bayonne station to hotel. After two days of planes, trains, and buses…….I was not too proud to take a short taxi ride :-)

Easy Jet flies CDG to Biarritz once or twice per day, sometimes early and sometimes late. To make that connection, you have to collect any checked luggage, go through passport control (where there can be long lines), and re-check luggage if it's too large for Easy Jet carry-on regulations. Distances to change terminals at CDG are long, so I'd probably want 3 hours transfer time.

A few TGV trains per day depart direct from CDG TGV station in Terminal 2 toward Bordeaux (which is more convenient than going into the city to Paris Montparnasse station). The last of these that would get you all the way to Biarritz in one day is the 14:09, otherwise there's the 18:09 that would get you as far as Bordeaux. Again I'd want 3 hours transfer time and again you would loose your advance-purchase ticket cheapest when purchased 3 months ahead if you had any significant flight delay arriving into Paris.