The huge interior of the cathedral, with a central nave and four side aisles, is lavishly decorated. Gold is everywhere. But at the same time, there is a sense of overall simplicity and restraint in decoration, for the grand monuments are confined to the side aisles and the huge nave is left mostly empty.In the center is the great box-like structure of the coro (choir), which contains elaborate 15th-century choir stalls. The coro opens onto the Capilla Mayor, which is dominated by an incredible Gothic retablo (reredos or altarpiece). The supreme masterpiece of the cathedral was the life's work of a single craftsman (unfortunately it was under restoration at this time)