I spent my summer holiday in Brittany. Not an area I know well, but one with a rich history.
Brittany gets its name from the settlement of Britons from Wales and the west country who established themselves in the area during two migrations during the 9th Century. They fought off the Franks and established an independent state. Brittany during the Middle Ages is the story of fending off attempts to incorporate the Duchy into France. The French eventually triumphed in 1488.
We stayed in the Breton Marches, the borderland with France. It has several well preserved castles. The best is Fougeres. Established in the 11th Century it was developed over the next four centuries into an impressive fortification that is largely intact today. Well worth a visit.