Right on Ile Ste-Marguérite, Fort Royal is perfectly placed on the coast. It is famously known as the prison that locked up The Man in the Iron Mask in the 17th century. The identity of the prisoner was never disclosed and he died as the unknown man. The mystery of who he was, still lingers on. Now, this prison houses a museum that exhibits items recovered from shipwrecks and other parts of the region. But the main draw to the prison is the well-preserved cell that held The Man in the Iron Mask. The island is located just a short boat ride from Cannes.