Mynydd y Betws is a mountain or large hill located on the border between Swansea and Carmarthenshire in South Wales, between Ammanford and Clydach. It is an area of upland with large stretches of tussocky grassland. The medieval castle of Penlle'r Castell is located near the highest point and the Mynydd y Betws Wind Farm is prominent with fifteen 110 m (361 ft) wind turbines. It is a UK listed Marilyn.
Penlle'r Castell - Visible at this site are a series of impressive earthworks with deep ditches and some fragments of the stone buildings that must have topped them. It may have had two stone towers, probably made of dry stone walls because there are no signs of any mortar having been used. It may not have been permanently manned.