Llanddeusant is a community in the Black Mountain Range of the Brecon Beacons National Park in Carmarthenshire, Wales.

The boundaries were changed and most of the population was shown under the Llangadog community.

The village lies below the prominent north-facing scarp of the Black Mountain and the glacial lake of Llyn y Fan Fach.

In the west, the route climbs to Carreg Cennen Castle and Garn Goch.

The route finishes at the railway station at Llangadog having formerly stopped at the village of Bethlehem (51°54′35″N 3°54′48″W / 51.9098°N 3.9132°W / 51.9098; -3.9132 (Beacons Way, western trailhead)).