Pen y Fan (886m) and Corn Du (873m) are the two highest peaks in the Brecon Beacons, Powys. Formed from different bands of Old Red Sandstone the mountains have been massively eroded to form scalloped escarpments and deep corries or 'cwms', which are typical of a glaciated mountain landscape. This area is a part of the Fforest Fawr Geopark.