Carl's directions are spot on, almost, I would just add park by the trees and hop over the fence. This cairn is bigger and less despoiled than its near neighbor to the west, Pant Madog, and there's no trig point to get in the way. According to Coflein it is a meter higher than Carl's approximation, which accords well with what we saw. But neither of them mention the wondrous views north and east over Trecastle and Sennybridge. Trees once more obscure views to the distant Brecon Beacon mountains.
A good cairn apparently undisturbed, if there were no stone circles round here this would be my sitting and pondering place
The Cairn is not visible from the road.
Taking the minor road west out of Trecastle (heading towards Y Pigwrn stone circles) you first pass a turning on the left which leads to Penrhiw Farm. Keep on the road towards the stone circles and you shortly come to two metal field gates on your left hand side. Stop at the first gate and climb over the metal fence opposite - no barbed wire for a change! Walk up the small embankment and you will see the cairn, only a short walk away. The Cairn is approximately 10 metres in diameter and 0.5 metres high.
Note – the Cairn is not visible from the road.