Hay Bluff (Welsh: Penybegwn) is a prominent hill at the northern tip of the Black Mountains, an extensive upland massif which straddles the border between south-east Wales and England. The mountain sits on an escarpment which faces north and runs roughly east-west, the next peak in the west being the Twmpa. The flat summit of Hay bluff overlooks the middle Wye Valley and the book town of Hay-on-Wye is marked by a triangulation pillar at a height of 677 metres (2,221 ft).