The Île Sainte-Marguerite is the largest of the Lérins Islands, about half a mile off shore from the French Riviera town of Cannes. The island is approximately 3 kilometres in length and 900 metres across.
The island is most famous for its fortress prison, in which the so-called Man in the Iron Mask was held in the 17th century.
Wikipedia https://en.wikipedia.org/wiki/Île_Sainte-Marguerite
Coordinates 43°31'9.141" N 7°2'58.603" E
