Glasfynydd Forest, an extensive area of coniferous plantations in the west of the Brecon Beacons National Park in Wales, straddling the border between Powys (Brecknock) and Carmarthenshire.
The forest is divided into three blocks, the northernmost of which encircles the Usk Reservoir near the head of the River Usk. The southernmost is the largest block occupying the ground south of the Usk valley and to the west of Crai which rises to Moel Feity. The smaller central block lies to the south of the minor road between Trecastle and Llanddeusant at Mynydd Wysg.
The largest block was photographed in part during RCAHMW aerial reconnaissance in June 2014.
Additional source: https://en.wikipedia.org/wiki/Glasfynydd_Forest

RCAHMW, 31 July 2017