Built by Ferdinand of Aragon between 1485 and 1498 in direct response to the Turkish siege, the castle is a low, massive pentagonal structure with three cylindrical towers and a deep moat. It sits at the southeast corner of the old town walls, guarding the harbour entrance. The fortifications were designed to absorb cannon fire — thick, sloping walls and squat profile mark the transition from medieval to early-modern military architecture.
Inside, the rooms host rotating exhibitions of art and archaeology. The ramparts can be walked for views across the Adriatic toward Albania. In summer the castle is also a venue for concerts and the Otranto Film Fund Festival.