Take the Ouigo Train to Rennes. From the Paris Montparnasse station, SNCF offers a number of direct TGV trains to Rennes. The lowest cost option is the morning Ouigo train, which costs about $20 for a one-way ticket. The regular SNCF trains are much more expensive and cost $80-100 for a one-way ticket.
Download the Ouigo App. The Ouigo train I traveled on was clean and comfortable. I paid a nominal fee for the large luggage I brought on board and also opted for the seats with an electrical outlet. Installing the Ouigo app was essential since I did not have access to a printer. I could just show my boarding pass from my phone.
Rennes to Mont Saint-Michel Bus. The journey from Rennes train station (Gare de Rennes) to Mont Saint-Michel is serviced by a bus that runs four times a day: 9h45, 11h45, 12h45 and 16h45. So, the morning Ouigo train (7h06 – 9h07) is perfect for catching one of the connecting buses. The noon Ouigo train (12h14 – 13h53), on the other hand, drops off passengers right in the middle of the afternoon gap. If you don’t want to wait 3 hours, then the alternatives are hiring a private car or renting a car.
Tidal Schedule. The Mont Saint-Michel Tourist Office publishes a tide schedule, if you want to plan your visit around high tide. I visited during low tide and it was quite dry around the island, except for that sliver of water I found that created the perfect reflection.
Hotels. Staying overnight at Le Mont-Saint-Michel offers a number of advantages. In the evening, once the crowds depart, the restaurants and shops begin closing and the streets empty. As the pace slows, I was able to walk around the island without having to navigate through a sea of fellow tourists. During these hours, it’s easier to compose photos with nobody in them.
Shuttle Bus. The complimentary navette travels from the parking lot to Mont Saint-Michel, with a stop at the off-island hotels and restaurants. The bus (and pedestrians) both cause vibrations on the bridge as they pass by. If you are using a tripod for long exposure photos, you need to take that into account.