Llyn Cwm Llwch both Pen y Fan and Corn Du and indeed from the spur of Pen Milan to its west. Llyn Cwm Llwch Llyn Cwm Llwch () is a small lake or pool in the Brecon Beacons National Park in Powys, Wales. It is between 1 and 2 acres: much smaller than the two glacial lakes in the west of the Black Mountain (range): Llyn y Fan Fawr and Llyn y Fan Fach. It is of glacial origin, occupying a rock hollow beneath the peaks of Pen y Fan and Corn Du in the central Brecon Beacons. It is drained by the
Pen Llithrig y Wrach underfoot, or because of the resemblance of its pointed profile to an archetypal witch's hat. It is an outlier of the Carneddau, the higher peaks of which can be reached from Pen Llithrig y Wrach via Pen yr Helgi Du. On its eastern side, the mountain slopes steeply down to Llyn Cowlyd. It may be climbed from the southern side, from Capel Curig or the A5, or from the north-east, from Dolgarrog or Tal-y-bont in the Conwy valley. It is quite prominent when viewed from the north near Llandudno. Pen Llithrig y Wrach Pen Llithrig y Wrach is a mountain