Fforest Fach is a small area of unenclosed land within Brecon Beacons National Park southwest of Sennybridge in the county of Powys, Wales.
Some of the sandstone beds on the north-eastern spur of the hill have been quarried in the past for building stone or possibly for use as roof tiles.
The now disused Pantymaes Quarry is a major working of the sandstone on the eastern side of the hill which is readily seen from the road.
A legacy of the glaciation of this area during the last ice age is the presence of glacial till around the flanks of the hill.
[1] The summit plateau of the hill is open country across which walkers may wander at will.