Its crenellated wall flanked by square towers is dominated at one corner by a high keep. A spiral staircase takes you to the first floor, whose attractive star-ribbed vaulting rests on Moorish-style honeycombed corner squinches. A gallery over the machicolated parapet runs the length of the wall, just below the top of the castle, which is a remarkable lookout point over the Alentejo wheat plain.