Caen to Mont Ste Michelle

Apart from any possible misinterpretation of what you mean by "quick",
and what you are trying to compare (use of time, mode of transportation, etc)
as a "good idea", yes, if you are in Caen, a day trip to MSM is a fine thing to do.
Might not have to be a full day, but no reason it can't be.

There are historical posts in the forum on the access, parking, logistics, etc.

We took the train from Paris to Rennes, then picked up our rental car at the train station to head to Mont St Michel. Super easy and convenient one hour drive. But Caen would work too.

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And you can visit Bayeux too. The D-Day beaches are nearby.

Hi,

I think it's a great idea. I did the same back in about 2016. Rented a car near the Caen train station and drove east. I think the rental car company was "euro car?" I believe it was about 1 hour 30 minutes and worth every penny and every second. You won't regret it.

If you do it, do not think it will be quick if you leave mid-morning for a mid-day visit. You will hit the crowds at their worst, and it is an hour and a half each way by car. I would plan a visit for early in the morning (departing MSM by 11:00am) or late in the day (arrive MSM around 4:00). Otherwise you may as well join a tour bus, as you will be there when all of those hoards are there anyway. But the place is very special and worth a visit. Just much better if you can spend the night on the Mont and have the place to yourselves late at night and early in the morning.