The parish church of St Mary's, hidden among the lanes inside the walls, is one of the largest medieval parish churches in Wales. Its tall, slender spire — visible from miles offshore — was a navigation mark for sailors entering the harbour. Most of the present building dates from the 15th century, when Tenby was at the height of its medieval prosperity.
Inside, the wagon roof of the chancel is the standout, decorated with hundreds of carved bosses. Robert Recorde, the 16th-century mathematician who invented the equals sign, is buried somewhere on the site, though the exact location is unknown.