Crug Hywel is an Iron Age Celtic hillfort,[1] with a clearly visible earth and stone ditch and rampart.

[2] 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.

Located at the southern edge of the Black Mountains in south-east Wales, it rises to 451 m above sea level, from the southern flank of Pen Cerrig-calch (701 m), and overlooks the town of Crickhowell, whose name derives from Crug Hywel.

The whole mass of rocks forming this outlier of Pen Cerrig-calch can readily be seen to dip more sharply to the south than nearby strata and is considered to be an excellent example of a translational slide.