Waun Lefrith is a top of Picws Du and is also the westernmost of the Carmarthen Fans or Bannau Sir Gaer, a group of peaks within the Black Mountain (Y Mynydd Du) of the Brecon Beacons National Park (Parc Cenedlaethol Bannau Brycheiniog). It lies within Carmarthenshire, Wales. The summit plateau of the mountain reaches a height of 2221 feet above sea level. Picws Du and Fan Foel are the other, higher summits of the Bannau Sir Gaer / Carmarthen Fans. The glacial lake of Llyn y Fan Fach dominates the panorama to the north of the peak. Beyond the lake to the north lies the Usk Reservoir and then the Cambrian Mountains on the horizon. Swansea Bay and the Bristol Channel are visible to the south across the undulating dip slope of the mountain. The Tywi valley lies to the west, with Llandovery and Llandeilo as important market towns