ridge is a number of hummocks and hollows, part of an old quarry, and you can look down past a rowan tree growing out of the crags to Cwmcynwyn Farm. There is a rock outcrop here with bedding showing clearly.
From the pools on the summit of Allt Ddu drop down past the stones of the quarry towards the Plas-y-gaer settlement. Just on the edge of this hill there is a distinctive furrow in the hillside which is an old quarry path. Continue down this path (marked with a dotted line on the map) towards the settlement, descending the front of the ridge. The descent of this ridge provides a good view of the settlement with the earth bank being now planted with a line of large trees.
Plas-y-gaer is an Iron Age settlement some 2000 years old, gaer meaning fortress and plas meaning place. The site is unexcavated but was probably built to defend the surrounding fertile land. There are surviving earthworks forming an oval shape and the height of the main rampart varies between 2 and 3.2m. As there is no sign of an entrance, access was probably gained from the north. No ancient features are visible in the interior.
At the bottom of the slope turn left in front of the settlement. As you come round the corner of the settlement follow the path diagonally down to the left, arriving at a stone wall, where there is a finger post and gate. A track leads to the farm (Plas-y-gaer). At the farm turn left through a gate and right into a field at the blue waymark post.
From here head across the field to a line of pylons reached through a gap in the trees. Turn right at a line of trees and walk up to a gate and stile in the right corner of the field. After crossing the stile, descend a shallow valley to another stile which you will see in the field about 60m in front of you. Follow the wire fence on the right-hand side downslope to the derelict buildings. Walk to the left of the farm buildings to a stile in a fence and onto a track. At the end of the farm track is a gate beyond which is a tarmac road. Turn right on the road and drop down the hill to the start at Pont Caniedydd.
WALK 5
Cwm Sere and Bryn Teg
| Start | Pont y Caniedydd (SO 039 244) |
| Distance | 11km (6.5 miles) |
| Total Ascent | 641m (2103ft) |
| Map | OL12 Western Area |
A classic route from the north side of the Beacons and well worth choosing for a first visit. It includes a superb valley walk with small waterfalls, a climb up the head wall, a detour to the highest peak of Pen y Fan, return via Cribyn and the Bryn Teg ridge. There are good views of the Beacons themselves, the Black Mountains and even of Cadair Idris to the north on a clear day. Route finding, as in all high places, may require map and compass and the final climb to the summits can be hard going. There is particular interest in the glacial geomorphology of the U-shaped valleys.
From the car park turn right (N) along the road for 100m to where it bends to the right (NE) and flattens out at the crest of a hill. Leave the road through a gate, taking a track to the left (W). The track leads to Pant Farm after 200m and then curves round to the left in front of the buildings.
Look left (SW) for a good view of the north-east face of Pen y Fan with Cwm Sere in the foreground beyond the trees. On the left is Bryn Teg ridge leading up to the prow of Cribyn. This will be your descent route. On the eastern side of this ridge is the brown scar of the Roman Road running over Bwlch ar y Fan which runs between Cribyn and Fan y Big. Looking back the way you have walked, the escarpments of the Black Mountains are visible on a clear day.
Continue on this track, leaving the buildings on your right, and climb steadily up the slope through a gap between hawthorn hedges. Bear right and then left, continuing in the direction of Cwm Sere to Croftau. Leave the house on your left, pass through the gate and a large oak on the right and keep to the left-hand side of the field to another gate where you enter Cwm Sere proper. The woodland on the far side of the stream on your left is managed by the Brecknock Wildlife Trust (see Walk 7).
Continue through yet another gate along the obvious track leading into sparse woodland and across to a gap in the tree line. Continue across the field for 300m to a line of trees in front of you. In the centre of this barrier is a gate leading to a track which bears slightly right past moss-covered ant hills and through mixed woodland of beech and hazel. Deciduous woodland attracts varied birdlife and, depending upon the time of day and season, you may see woodpeckers and owls as well as other typical woodland species.
The track is easily followed as it drops through the woods, crossing a small stream running down from the right. At the end of the woodland is the hill fence through which a gate leads out onto the hillside, opening up a magnificent view of Cribyn on the left and Pen y Fan straight in front. Drop into the stream bed and follow this upstream, encountering small waterfalls on the way towards the headwall at the end of Cwm Sere between the north faces of Pen y Fan on the right and Cribyn on the left.
Pen y Fan from Cribyn
You can expect to see dippers in the stream bed and, with luck, a buzzard wheeling overhead or a heron hunting its prey near the water. Cwm Sere was carved by ice into a U-shape but this has been altered slightly by a snowbed eating away at its western side in post-glacial times (see Walk 4) and by Nant Sere eroding away a notch in its base (see ‘Glacial origin of U-shaped valleys,’ Introduction).
Once in the basin below Cribyn strike across towards the foot of the north-east face of Pen y Fan. The sheer immensity of the north-east face of Pen y Fan can be fully appreciated from the head of the cwm.
GEOLOGY AND GEOMORPHLOGY OF PEN Y FAN
The north-east face of Pen y Fan rises some 380m (1200ft), becoming vertical near the top where the more resistant Plateau Beds form a distinctive cap to the summit. Units of the Lower Old Red Sandstone, Plateau Beds and Brownstones are well exposed in the face. The ribbed nature of the Brownstones is due to the alternation of sandstone with softer marls. The brown scars on the face of the mountain are testimony to the relentless onslaught of the elements and the processes of erosion. The most deadly of these is freezing and thawing of water in cracks in the rocks, which literally shatters the stone along existing lines of weakness. (The Brownstones are particularly well bedded and cleaved, and split apart forming regular blocks, seemingly made for constructing dry-stone walls and buildings.) Gravity then plays its part in transporting stone and soil downslope. Rainwater percolates into the ground where it is concentrated along the upper surfaces of the less permeable marly layers. Eventually it seeps out of the face, leading to erosion of the soft marls. This undermines the sandstone blocks above, leading to their collapse. This water is then concentrated in gullies, further eroding soil and rock which is then channelled to the bottom of the face, where it spreads out to form talus cones. Look out for a distinctive white, frothy stream which forms in the large gully on the right of the face after heavy rain. In snow and ice conditions, the gullies provide spectacular winter climbing routes for daring climbers using crampons and ice axes.
Ascending the steep prow of Cribyn
From the foot of Pen y Fan take the track up the headwall which goes from bottom right to top left. Crossing piles of loose stones at first, the headwall track rises at an easy angle, presenting no problems, and arrives at the unnamed col between Cribyn and Pen y Fan. The extended route to the summit of Pen y Fan leaves from here. There is also an exhilarating alternative route round the shoulder of Cribyn that may be followed from here.
Turn left (E) up the steep, eroded slope to the summit of Cribyn. The ascent of Cribyn is rewarded with an impressive panorama on a clear day, with good views to the west of the north-east face of Pen y Fan and