 Dolbadarn Castle comprises a courtyard , surrounded by a number of towers and a round keep . The castle is built from purple and green slate stone , mainly constructed in a dry stone fashion without mortar , with the exception of the keep . The courtyard follows the natural shape of the hill and is protected by a curtain wall ; originally perhaps 15 feet ( 5 m ) high , it is now only at most 3 feet ( 1 m ) high . Of the castle buildings , only the keep remains to any significant height . 
