Castillo de San Marcos is a miniature version of the massive Fort San Cristobal in Puerto Rico – access is by way of two draw bridges over a dry moat – the ‘moat’ being the outer defense works to the fort itself, and a killing field if anyone crossed it during a siege. A detached bastion is the first part you walk over to, and then across another bridge to the fortress itself.
The main citadel is laid out as a four-pointed star, with thick coral walls angled sharply up to grant it more mass. The exterior is a black-grey color, each block eroded away to its center, as the stone is softer than the mortar that holds it in place. Inside the thick walls, huge arched rooms, each two stories tall and some forty to fifty feet thick fill up the space between the outside, and the interior white courtyard and its square patch of green grass. A modest house might have been able to sit there in the center and fill the space up.