Clogwyn y Garreg, a small outcrop to the south-east of Mynydd Mawr, from the shores of Llyn Dywarchen, Eifionydd, Snowdonia (August 2009).
In his Itinerarium Cambriae (1191), Geraldus Cambrensis wrote that Llyn Dywarchen had "...a floating island in it, which is often driven from one side to the other by the force of the winds; and the shepherds behold with astonishment their cattle, whilst feeding, carried to the distant parts of the lake