This advanced defensive structure features a central redoubt with three gunpowder magazines. Around its outer perimeter are vaulted spaces that once served as storage rooms, troop quarters, and two cisterns. It also includes three cells or dungeons.

Cannons were installed on the upper level to defend the seafront. During the presidency of Porfirio Díaz, this area was converted into a prison. Access to it is via a bridge known as the “Bridge of the Last Sigh,” named for the grim fate of many who entered: due to the unsanitary and overcrowded conditions, few prisoners made it out alive.