Cadair Fawr is a hill in the northern corner of the county borough of Rhondda Cynon Taff in south Wales. It lies within the Brecon Beacons National Park and Fforest Fawr Geopark. The 485m high summit at OS grid ref SN 978123 is marked by a trig point. Cadair Fawr is the highest point of a broad ridge known as Cefn Cadlan which forms the northern edge of Cwm Cadlan, a valley which itself runs east-northeastwards from the village of Penderyn. The name Cadair Fawr signifies the 'big chair' whilst Cefn Cadlan signifies the 'ridge of the battlefield'.