I have managed to figure out how to get from CDG to St-Michel via REF Route B. Can someone tell me if it is best at this point to take a cab to Gare d'Austerlitz or is it easy from the St Michel N-Dame station to get on the yellow line (C) and take the metro to Gare d'Austerlitz?

Also, coming back to Paris from Souillac I will need to get from Gare D'Austerlitz to the Chatelet Les Halles stop - should we taxi that or will the yellow line (C) connect to the blue line(B) at St Michel?

thank you in advance for your advice.

Just change at Saint-Michel to the RER C and go straight to Gare d'Austerlitz.

Coming back to Paris just do the reverse. Take RER C from Austerlitz to Saint-Michel and change to RER B to Les Halles, which is the first stop. You could also take Metro line 4 from here to Les Halles. There are a couple stops along the way but Metro trains tend to run more frequently than RER trains.

Let me just add something because I see that maybe you are wondering how difficult it might be to find your train at a transfer. The RER C can be a bit confusing for making changes as far as finding the proper direction. Going from Saint-Michel to Austerlitz you want to look for signs for RER C in the direction of Versailles-Chantiers. There are other directions that will be mentioned along with this destination but to keep it simple I'll give you one direction to watch for. From Austerlitz to Saint Michel look for RER C in the direction of Versailles-Rive Gauche (again, other directions are also listed). At Saint-Michel look for signs for RER B in the direction of Aeroport Charles de Gaulle.

It might be a lot easier to take the Air France bus from CDG to Gare de Lyon and simply walk (or take bus 57) across the Seine to Austerlitz.

Do the above in reverse when you return.

Going from Saint-Michel to Austerlitz you want to look for signs for RER C in the direction of Versailles-Chantiers.>

you can also hop on RER C trains labeled St-Martin Etampes (or some wording similar to that with the terminus town, Etampes, in it) - some trains go to Versailles-Chantier perhaps but more, many more go to St-Martin d'Etampes and these will not be labeled Versailles-Chantiers.

Yes, escalators will take you from the RER B, which is far underground, to the RER C, which runs directly under the street. The screens show all of the stations where the trains stop, so it is easy to spot 'Gare d'Austerlitz' as the first stop from Saint Michel.

Actually, you could walk it if you don't have a lot of luggage. From the Saint-Michel Metro to the Gare de Austerlitz is just 1.9 km and would take 27 minutes to walk, according to Google Maps. Even coming back is not too far; 3.1 km, and 39 minutes from the Gare to Chatelet.

The instructions for Versailles-Chantiers had to do with the signs pointing directions to the right platform, not the destinations labeled on the trains themselves.

However, in addition to Versailles-Chantiers and Saint-Martin d'Etampes you can also look for Massy-Palaiseau and Dourdan-La Forêt.

In the other direction besides Versailles-Rive Gauche also look for Château de Versailles and Saint-Quentin en Yvelines.

Actually, you could walk it if you don't have a lot of luggage.>

I have walked this route literally hundreds of times and it is along a wide sidewalk the whole way - if you had time to spare you could walk along the Seine paths thru the outdoor scultpure park lining the Left Bank quay. austerlitz station is currently being completely rehabbed so may seem a bit chaotic upon first glance. If you are buying tickets for the train south then you would get an RER transfer ticket as part of the over all price I believe.

Great advice everyone, and thank-you all for the details! We are looking forward to riding the 'tube' and think this will be a great experience for the kids (16 & 12) as we don't have a subway system in Denver CO!

They only call it the tube in London. Definitely not in France (even in French, just don't call it that).

RER C is not even in a tube but simply a slightly underground railway that is for the most part open to the skies at the top.

True. It is only completely enclosed around places like Musée d'Orsay. That's why it gets closed for a certain amount of time almost every spring when the Seine floods it.

Speaking of which, with all of the recent snow melt and rain, the Seine has gotten very high, which could affect the RER C, the left and right bank expressways, and the bâteaux mouches which can't get under the bridges when the water is too high.

I don't know why they even call it a tube in London. We have one where I live (Wash DC) named like in Paris (called the metro) and it's just a train run in tunnels (or on elevated tracks in some areas), just like in Paris. It isn't in any tube even when underground.

I don't know why they even call it a tube in London.>

come Christina have you ridden the Tube in London - the trains typically fit just into a tube-like tunnel, with very little room to spare - a real tube - this is why in stations down the line you can feel the air swooshing when a train approaches. London's Tube does indeed for the most part on the older main lines in central London run in a tube.

... and I can't get it out of my mind in case of an emergency, since there is no way to evacuate except through the train. I do understand that engineering techniques at the time were limited, but it would seem reasonable for London Transport to create emergency bays or something in the tunnels, just in case.

Okay, back to Austerlitz now.