In the south east of the island, 12 km from the Trion Guen campsite, visit Locmaria, and in particular its church dating from the 11th century.
Locmaria is the most "natural" commune of Belle Île En Mer and harbors many myths and legends. More anecdotally, the place has inspired certain writers such as Alexandre Dumas. In his novel "Le Vicomte de Bragelonne", he kills one of his three musketeers, Porthos, in the cave of Locmaria.
You will find more information on the website of the tourist office:
Photo credit: photo 2 CRT Bretagne - Emmanuel Berthier