Funded and organised by Cadw, the festival annually offers free entry to an array of museums, heritage properties and unusual landmarks through the month of September.
Mae’r ŵyl, sy’n cael ei hariannu a’i threfnu gan Cadw, yn cynnig mynediad am ddim i ddewis eang o amgueddfeydd, eiddo treftadaeth a mannau anarferol drwy gydol mis Medi.