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 y Clawdd Castle a medieval fortified site rather than a castle. Pen y Clawdd Castle Pen y Clawdd Castle is a ditched mound with a double moat, roughly circular in shape, with a diameter of approximately 28m to 30m and about 2.4m high. The castle is in Llanvihangel Crucorney, about five miles to the north of Abergavenny, Monmouthshire, in south east Wales and lies between the Usk and Monnow rivers. The mound was designated a scheduled monument in 1950 and described as a defensive medieval motte. The castle mound is adjacent to Pen-y-Clawdd Court (a Grade I listed building), a stable and cowshed