That's easy to answer, there are many spots within France, one of my favorites is in the Normandy region, in an area named La Manche ( on the Cotentin Peninsula) . La Manche is the French name for the English Channel (Which it thrusts into)
This area just west of the major D Day beaches, is a pretty and wild rural area of Normandy. Some people have called it a version of Ireland. The area stretches from Mont St Michel; to Cherbourg. Its home to charming seaside towns and villages, it has a rich maritime heritage and is home to many WW2 battles beyond the D Day beaches.
If you are looking for drop dead landscapes, largely undiscovered by tourists than look no further from here.