Pen y Fan via Cwm Sere
SO025248 From the 1 main car park, follow the footpath down into the stream valley of Nant Gwdi, cross the bridge and climb up through woodland to the open hillside. Turn left and follow the path above the fence into the valley, to where it drops down to the stream. Pick an easy descent and work your way along Nant Sere to the head of the valley. At the head of this valley is the north-east face of Pen y Fan on the right and the north-west face of Cribyn on the left.
SO019216 Once in 2 the basin below Cribyn, strike towards the foot of the north-east face of Pen y Fan, and from here climb the headwall on the track which starts from bottom right and continues to top left. You will cross piles of stones brought down the gullies by winter frosts. The headwall track rises at an easy angle and arrives at the unnamed col between Cribyn and Pen y Fan.
SO019211 From the 3 col climb steadily (west), following the line of Craig Cwm Sere to the summit of Pen y Fan. The final ascent to the summit of Pen y Fan is up a very stony area, and the National Trust has built a zigzag path, known as Jacob’s Ladder, up this steep slope to the top. The impregnable north-east face protects one of Britain’s true botanical treasures from grazing sheep. The combination of high altitude and a shaded northern aspect creates living conditions more akin to polar latitudes than to temperate southern Britain. Extensive ledges high up on the face are crammed full of interesting and unusual species that bring the otherwise bleak and foreboding crags alive with vibrant colour in spring. Walk across the flat surface of Pen y Fan to the trig point. This can be found in bad visibility by carefully following the north-east crag line, the trig point being located at the end of this on the left. The north-east face is very steep and care must be taken not to stray too near the edge, especially in strong southwesterly winds or when corniced in winter.
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Leave the summit of Pen y Fan by carefully scrambling (northnorth-east) down the exposed Plateau Beds. The rocks can be slippery but the route drops quickly to the fine ridge of Cefn Cwm Llwch. Once on the flat section of the ridge, look across to the east for a magnificent view over the ridges of the
Beacons and the triangular profile of Cribyn. Cwm Sere was carved into a U-shape by ice, but this has been altered slightly since the last Ice Age. On the left there is a distinct step in the valley side, a post-glacial feature known as an anti-planation terrace, while Nant Sere has also been eroding away a notch at its base. Follow the path along the flat ridge, leaving it when it drops gradually to the valley of Cwm Gwdi. Keep to the eastern edge of the ridge, following a path through some boggy areas with mainly heather, past the disused quarries and onwards to Allt Ddu.
SO027241 From the 5 pools on the summit of Allt Ddu, drop down past the stones of the quarry north to the path above the hill fence and follow retrace your earlier route back to the car park. The descent of this ridge provides a good view of the Plas-y-gaer settlement with the earth bank now planted with a line of large trees.