St Mary's Collegiate Church is one of the oldest and finest medieval churches in Ireland still in regular use, with parts of the structure dating to the 13th century. The interior is cool and shadowed, with magnificent stone carvings, medieval tombs, and a striking chancel that has survived remarkably intact despite centuries of war and neglect.
The churchyard is worth wandering: the walled garden and the stretch of 13th-century town walls that run alongside it create an atmosphere you rarely find. Entrance is free and the church is generally open during daylight hours. Worth an unhurried half-hour.