What is the best way to travel by train to Mont St. Michel? How long does it take?
No train goes all the way there. People posting here either drive, or take the train and then bus. Pontorson-Mont St. Michel is the nearest train station, there's a bus connection from there to the Mont. For details on the latter option, check Rick's book France, or follow the search procedure given in the Site FAQ click here to find prior discussions of the details.
Kent gave you one route, but there is another that is slightly better. Take a train from Gare Montparnasse to Rennes and a SNCF (French National Rail) bus from there right to Mont-Saint-Michel. The trip takes a little under four hours. See the timetables on the German Rail site, www.bahn.com/i/view/USA/en/index.shtml. Enter Mont St Michel as your arrival point rather than Pontorson.
Tim: Thank you for the correction and further information. As many of you know, Tim is our long-time train guru, consistently giving accurate advice over a number of years here.