Occupying the oldest part of the Fort Royal on Sainte-Marguerite Island, the Musée de la Mer is a land and marine archaeological museum.
The museum is laid out around the former prison with the cell in which the Man in the Iron Mask was locked up, the Roman cisterns of the old castle and, upstairs, its collection of objects from Roman and Saracen shipwrecks as well as Roman frescoes. The museum also presents explicative scale models and works of contemporary art. Its temporary exhibitions take place in summer on the vast terrace overlooking the sea.