The Castle, in its initial configuration from the late 15th century, was quadrangular (a right trapezoid) with four “Rondelle” (circular towers) at its corners. The one facing the sea was more prominent, as often depicted in treatises by Francesco di Giorgio Martini. The configuration we see today is the result of constant modifications throughout the 16th century, driven by the continuous evolution and refinement of firearms.

The castle is surrounded on all sides by a deep moat, crossed at the entrance by a bridge. This bridge currently features a stone arch and a wooden walkway, but was likely a drawbridge originally. A narrow corridor leads directly into the ground floor atrium. As you cross it, you’ll notice the thickening of the facade, a modification made in the early 16th century. All the ground floor rooms, built against the outer curtain walls, are rectangular or square and open onto the inner courtyard, covered by vaulted ceilings.

Outside the original quadrangular structure are two rooms, certainly among the most representative of the entire building: the triangular and rectangular halls. The triangular hall was created by mid-16th century expansions when the bastion was added externally between the two Rondelle. The vaulted ceiling of this hall is particularly striking, defined by the intersection of three carparo stone pavilion groins that follow the unique triangular shape of the room’s floor plan.

The Chapel on the ground floor is partially frescoed and contains various frames and epigraphs, including those from the tomb of Donna Teresa De Azevedo, who died on February 23, 1707. Her husband, Don Francesco de la Serna y Molina, the castellano at the time, dedicated a very tender epigraph to her, calling her an “example of modesty, goddess of beauty, model of honesty, offspring of Spanish heroes.”

Below the ground floor lies an intricate network of tunnels, galleries, and small rooms, forming the “underground” system. These are highly historically valuable and evocative spaces, remaining largely unchanged since their construction in the late 15th century. Only a few passages underwent minor transformations and expansions in the 16th century due to the advancement of firearms. The underground levels are where it’s easiest to trace the different construction phases of the Castle: the initial late 15th-century layout, the early 16th-century linings and reinforcements of the curtain walls and some rondelle, the addition of the mid-16th-century triangular bastion, and finally, the construction of the late 16th-century sea-facing buttress.

A covered stone staircase and an external stone staircase lead to the first-floor gallery, providing access to a series of rooms that largely mirror the layout and position of the ground floor. From this level, however, you can access the interior of the three rondelle still present at the corners. In the heart of these rondelle, protected by a thick outer curtain wall, are circular rooms covered by hemispherical carparo stone domes, where bombards and cannons were placed, aimed through gunports communicating with the exterior. The roofs feature patrol routes, protected by very thick walls with loopholes for cannon placement.

Both on the external curtain walls and inside the atrium, there are several heraldic coats of arms belonging to sovereigns and nobles who played a significant role in the Castle’s history. Of particular interest is the one above the main entrance gate, featuring the sculpted coat of arms of Emperor Charles V. The fortress is also the setting for the first gothic novel in history: The Castle of Otranto by Horace Walpole (1764).