GR 223
The GR 223 is a French hiking trail in the Grande Randonnée network.
Understand
It is known as Sentier des Douaniers ("Custom Officers' Way"); the route is mostly coastal.
Prepare
Get in
Walk
It goes all the way from 1 Honfleur to Mont Saint Michel via the coast of Calvados and Cotentin (Mont Saint Michel is on the Breton border in the west). The entire walk takes a month, but most people prefer to pick sections according to their interest.
The first part of the walk goes west past some coastlines including the 2 Côte Fleurie (literally, "Flowery Coast") and the 3 Côte de Nacre (literally, "Mother of Pearl Coast"). Farther west, history fans often choose to visit the D-Day beaches, while lovers of nature (cliffs and coves) prefer the walk around 4 Cap de la Hague, west of 5 Cherbourg, and others still opt to approach Mont Saint-Michel around its eponymous bay. The 6 Baie du mont Saint-Michel 
is the location of an amazing island and village.
Stay safe
Word has it that there are problems with cliff erosion over certain sections, so don't be surprised if you are diverted inland at some points.