Penwyllt (Welsh: "wild headland") is a hamlet located in the upper Swansea Valley in Powys, Wales, lying within the Brecon Beacons National Park. A former quarrying village, quicklime and silica brick production centre, its fortunes rose and fell as a result of the Industrial Revolution in South Wales. It is now an important caving centre. It is in the community of Tawe-Uchaf.