Departing England by ferry first stop was Saint Malo, not the most direct route but a great place to stop and have a walk about.
Taking the ferry over night is usually a good way to get a rest from driving and still make a few miles while avoiding some London traffic. The cabins aren't too expensive but for some reason the rooms were hot and dry, not much sleep for me.
The wall around the old town is completely walk-able with a few beaches thrown in that must be gorgeous in the summer.
I think we got pretty lucky with the weather, the crystal clear winter post rain air was just the ticket.