The 15th-century St Machar's, with its massive twin towers, is a rare example of a fortified cathedral. According to legend, St Machar was ordered to establish a church where the river takes the shape of a bishop's crook, which it does just here. The cathedral is best known for its impressive heraldic ceiling, dating from 1520, which has 48 shields of kings, nobles, archbishops and bishops. Sunday services are held at 11am and 6pm.