Castell Grogwynion on the north slopes of the Ystwyth Valley is 900 ft. O.D. and has been constructed on a prominent hill which rises precipitously from the river below. To the N.E. the ground falls away steeply to a tributary valley. The site in some particulars bears a resemblance to Castell Bwa Drain. The fortification of the two sites has been easy. They are unusually effective both on account of prominent positions and of the rock-ledges and scarps which provide ready-made defences.