Pen y Fan is the highest peak in South Wales, situated in Brecon Beacons National Park. At 886 metres (2,907 ft) above sea-level, it is also the highest British peak south of Cadair Idris in Snowdonia. It is the highest point of the historic county of Brecknockshire. The twin summits of Pen y Fan and Corn Du at 873 metres (2,864 ft) were formerly referred to as Cadair Arthur or 'Arthur's Seat'.

South Wales is a loosely defined region of Wales bordered by England to the east and mid Wales to the north. Generally considered to include the historic counties of Glamorgan and Monmouthshire, south Wales extends westwards to include Carmarthenshire and Pembrokeshire. In the western extent, from Swansea westwards, local people would probably recognise that they lived in both south Wales and west Wales. The Brecon Beacons National Park covers about a third of south Wales, containing Pen y Fan, the highest British mountain south of Cadair Idris in Snowdonia.