>>1930957gr 34, sentier des douaniers, start in Mont Saint Michel and goes all around the coast of Brittany.
GR tracks are really well made, well marked, and well deigned in terms of landscapes. My favorite paite is presqu'ile de crozon at the tip or Brittany, pic related
https://www.mongr.fr/trouver-prochaine-randonnee/suggestion/gr-34-du-mont-saint-michel-a-saint-maloif you want to take a look, but don't need to buy a map, you can find the gpx files or maps anywhere on the net,