Carreg Dwfn (also referred to as Careg Dwfn and Carregydwfn and referred to also as Careg-y-dwfan. ) is a hill four miles southeast of Llandeilo and just to the south of the village of Trap in the county of Carmarthenshire, south Wales. It lies at the western extremity of the Brecon Beacons National Park and Fforest Fawr Geopark.