Unusually, the trig point on this hill does not sit at the summit but 600 m to the south-west on a subsidiary spur.

On the southern slopes of the hill, sandstones of the overlying Plateau Beds Formation occur.

In common with other hills in the Brecon Beacons National Park Fan Fawr was subject to glacial action in the ice ages.

[3] The hill is within the Fforest Fawr Geopark designated in 2005 in recognition of the area's geological heritage.

The entire hill is open country, enabling walkers to wander at will, although most choose to take a line up from the car parks beside the A470 at Storey Arms and Pont ar Daf.