Ysgyryd Fawr is the most easterly of the Black Mountains in Wales, part of the Brecon Beacons National Park. It is 486 m high and lies just outside Abergavenny, near the English border. Its distinctive shape, comprising a long ridge orientated nearly north–south was caused by an ice–age landslip. The Beacons Way passes along the ridge.
There is a rich mythology attached to the mountain, including a distinctive stone known as the Devil's Table.
Ysgyryd Fawr has belonged to the National Trust since 1939. The ruins of an iron–age hill fort and a mediæval Roman Catholic church lie at the summit. Rudolf Heß used to walk here when he was held prisoner at Maindiff Court during the early 1940s. The name is sometimes anglicised to Skirrid Fawr, Skirrid or Skyrrid, and the mountain is also known as Holy Mountain or Sacred Hill.