Paris to Girona, Spain Train

It just a train. You can book Paris - Girona on www.sncf-connect.com. You get on in Paris Gare de Lyon, and get of in Girona. There us a part between Montpelier and Perpignan where the line gets close to the sea. For the rest it is just a normal TGV service.

The same train also goes to Barcelona.

I have taken the train from Paris to Barcelona. It takes about 6h45, meaning 8 hours door-to-door (including typical travel time to/from train stations), but flying takes 6 hours door-to-door, so the train is not that much slower! And for Paris to Girona, the train definitely has the edge, because flying involves using Beauvais airport which is far from Paris.
For a journey of that length, I find 1st class to be worth it, but the fares on the route can be high and French railway discount cards do not always apply.

Paris to Madrid by train is more ambitious; you have to change trains in Barcelona Sants (there is perhaps a possibility to change trains in Nîmes or Montpellier, transferring to the Marseille-Madrid train, but I am not sure) and it would basically take all day.

You will find a lot of info on the excellent Seat61 website, a great resource for train travel (esp. in Europe).

In addition to The Man in Seat 61, as linked above, there are loads of train geeks (said with love) on YouTube that would have videos of the route.

The French rail company SNCF has a few direct (no-change) trains from Paris that stop in Girona before continuing on to Barcelona. Travel time to Girona is just over 6 hours.

If the website doesn't respond to "Girona", use the French spelling of Gerone.

SNCF Connect

The Spanish train company RENFE is now running trains into France from Barcelone. They go as far as Marseille for sure, perhaps even Lyon. If not already as far as Lyon, they will be soon.

Great info! I really appreciate everyone taking their time to reply.