The Grotte Saint-Amand, not far from the Chapelle Notre Dame de la Paix and the village of Ker Borny.
This chapel, also called Chapelle St Hilaire or Chapelle St Amand, was built on the site of earlier chapels
and the Monastery St Hilaire,the "Champ du Cloître" that ruled Yeu island for three centuries, and was
destroyed in the 9th century.
The cave, the Grotte de Saint Amand (or Trou de Saint Amand) was used to hide holy and other precious items
in times of invasions and war.

Saint Amand (Amandus of Nantes or Amandus of Maastricht) was a French-Belgian-Dutch saint in the 7th century.
According to folk lore Amand freed Yeu island of a monster reptile that terrorised the island.
With the monster all other venomous snakes disappeared also, never to return to Yeu.