High Quality Content by WIKIPEDIA articles! Rhinog Fach is a mountain in Snowdonia, North Wales and forms part of the Rhinogydd. Technically, Rhinog Fach is a subsidiary summit of Y Llethr, missing Marilyn status by 3m. Thus making it a sub Marilyn along with Diffwys. To the north lies its higher cousin Rhinog Fawr, separated by the shapely pass of Blwch Drws Ardudwy.