Hi DMJohnson,
I have to take back what I said about the First Class Lounges requiring a subscription to the Grand Voyageur program.
If you have a TGV ticket that is both
first class and
Pro (TGV Pro 1ère), you have the right to enter the first class lounges, Salons Grands Voyageurs, on your day of travel, without need to be a part of the Grand Voyageur program.
In Paris the stations include:
Gare de Lyon,
Gare de l'Est,
Gare du Nord,
Gare Montparnasse.
Train stations outside of Paris with first class lounges: Bordeaux, Lyon (Part-Dieu), Lille (Flandres), Marseille (Saint-Charles), Nantes, Strasbourg.
These Salons Grands Voyageurs are generally open from 7am till 8pm.
You may have to pay for services inside, such as drinks, papers, Wi-Fi, etc. SNCF print materials don't specify which services are free and which are pay. Perhaps this is different, station to station.
Sorry for my mistake earlier saying that access to these salons always requires a membership card to Grand Voyageur.
Ben