When our ship docked at Le Havre, excursions were offered to Paris, Rouen, Honfleur and the D Day Beaches, but for some reason not to Mont St Michel. We booked with a local guide to take us there and had a wonderful day.
It is quite a climb up to the top of the monastery, but well worth it for the history and for the view. Then we stopped at a famous restaurant for lunch, all arranged by our guide. Although we like ship's tours in most ports, this is one of those instances where taking an independent tour makes sense and took us someplace that the ship's tours would not.
You can see some other tours we took on that British Isles cruise, both ship's tours and independent tours, at Royal Princess British Isles Pictures