Approach notes

Details taken from Wikipedia:

The Offa's Dyke national trail makes a steep ascent of the hill's northern slopes and then heads south eastwards along the broad ridge of the Black Mountain and the Hatterall Ridge. A more gentle path to the summit follows the crest of the north-facing scarp, known as Ffynnon y Parc, from the road summit about 1 mile / 1.7 km to the southwest at Gospel Pass. There is also a clear, but unpaved path which passes along the edge of the escarpment to the east with superb views over the countryside towards Hay-on-Wye. It leads to the trig point at the Black Hill (Herefordshire), and continues on to the south-east dropping down the stony knife-edge ridge towards Longtown. There is a small car park where the ridge drops into the Olchon valley, about 2 miles north of Longtown itself.