I am planning to do the same two days later. Would love to hear your granular, step by step plan. Perhaps my own heightened anxiety is interfering here, but I am finding it really challenging to see how to make connections on time. I arrive CDG 9:30am. Can I clear customs in time* to catch RER to ??? to get TGV to Bayonne? Do I need to purchase everything in advance? Is there a simpler path? *still no response from Demarches re health certificate; applied online the day it was offered, so I'm concern about possible delay at customs due to appropriate documentation of proof of vaccine. The Camino provides, and the pilgrim worries anyway...thanks for any insight, suggestions, tips
OK, deep breaths.......breathe in.........breathe out.......
The dawn rush at CDG customs is a crap shoot in my experience. Has been any where from 30 minutes to two hours, but you will have plenty of time either way. When you get out of customs, get ready for your first walk. Follow the signs that say Paris By Train, that will lead you to a staircase going down several floors. There are two types of ticket machines, and two ticket offices. To take the RER, which I do, you are looking for the Isle de France station and machines, not the Grand Lignes, which are the TGV's. I assume your TGV is later out of Montparnasse? There is a great briefing on how to do this here:
www.parisbytrain.com/charles-de-gaulle-airport-cdg-to-paris-by-train/ . Trains are frequent, walk up, buy a ticket, get on the next one.
You get on the RER heading into Paris. Depending on which one you catch (there are different types, some will make all stops, some will make fewer, and others will branch out south of the city to different locations. It does not matter in your case, they will all stop at your stop which is in central Paris. For Montparnasse, get off at Denfert-Rochereau station. For those unfamiliar with Paris, or directionally challenged, this is the hardest part. You are about six blocks from the TGV station when you get out of the station on the sidewalk. Walk northwest on Rue Froideveaux. You will pass a very large cemetery on your right. When you pass the cemetary, turn right, another block, and the station entrance is across the street on your left, you can't miss it. Total time from the RER station at CDG to standing in front of the TGV station in Montparnasse should be about 90 minutes. If you get turned around, ask anyone "Gare Montparnasse???" and they will point you in the right direction.
You should buy your TGV train ticket now. I like
www.thetrainline.com because they have an easy time with foreign credit cards, and they have the same prices as SNCF.
Buen Camino
PS: I would expect you to have time for a leisurely lunch at one of the many cafes around the station.
PPS: They have food on the train, but all the locals will grab a sandwich to go from the Paul's kiosk in the station. Best fast food in Paris!