I discovered the church of St. Mary, Tal-y-llin in the Shell Guide’s entry for Aberffraw.   It’s actually on a deserted road about three miles north- north-east of Aberffraw unmarked by the Ordnance Survey.   It’s a magical place, looked after by the Friends of Friendless Churches and miraculously open, not just to visitors, but to the fields.   Empty of any paraphernalia except a deep and rural piety:-