Crug Hywel is an Iron Age Celtic hillfort, with a clearly visible earth and stone ditch and rampart. Crug Hywel is approached by a couple of public footpaths across farmland from Crickhowell and Llanbedr and visited by the Beacons Way. It lies within an area designated as open country over which the public have the right to roam. The Welsh name Mynydd y Begwn is also used of this summit. As a result, it has been suggested that the name Crug Hywel (which means 'Hywel's mound') may originally have referred to the castle mound in Crickhowell.