Built in the 14C, the slightly leaning tower (total height 42m) is a veritable fortress. An external staircase leads to the superb octagonal-shaped Salle des Gouverneurs, which boasts an elegant rib-vaulted ceiling. There's a fine view of the harbour, the bay and Aix island from the upper platform in the watchtower, which is flanked by high walls with arrow slits and machicolations. In May, top divers compete in the world championships for their discipline, leaping from the top of the tower.