There is parking just below Castell Dinas at Pengenffordd a few miles south of Talgarth in the Black Mountains. Follow a well marked path onto the open mountain – visit the Iron Age hillfort of Castell Dinas if you have time – and then straight on up the steep ridge to the more level top ridge that runs along to Waun Fach – the highest peak in the Black Mountains – and Pen y Gadair Fawr just beyond it. Waun Fach itself is uninspiring, while Pen y Gadair Fawr has the more usual flat top of the Beacons mountains and a cairn on top which makes it a focal point for walkers.