From the same parking place as Foel Cae’rberllan the ridge up Gamallt is obvious, starting on the path from Pont Ystumanner. From the highest point adjacent to the forest, you need to fight your way a short distance through the trees to the summit lump. The easiest access is from a few yards further on (SE) where there is a gap between the trees.
(1hour 20 mins, 2 miles, 900’ of ascent)