is of little interest and avoids the superb waterfalls glimpsed earlier. Descend instead to the left and walk along the fence which soon reaches the stream. Here a small track crosses to the left bank although either can be followed to the waterfalls.
The hill fence crosses the stream ahead but there is a low-level stride over it just before the stream divides. The left branch of the stream is the more interesting and just ahead is an impressive waterfall. This can be climbed on the right arriving first at a small pool above the lower fall.
Climb up the right side of the upper fall or more easily up the hill on the right of the lower fall, reaching a series of smaller waterfalls from where there are magnificent views of Corn Du. When the stream starts to break up into many smaller tributaries, leave the stream to the right, striking westwards to the corrie lake of Llyn Cwm Llwch.
Llyn Cwm Llwch had an enchanted island only accessible through a tunnel from the shore. The island rose out of the water only on May Day when fairy flowers could be gathered to fairy music. The flowers were so lovely that a sacrilegious visitor brought some away with him and down the mountain. When they faded, the island disappeared below the waters and has never been seen again.
Cwm Llwch, Corn Du and Pen y Fan
From the northern end of the lake the path heads down the valley on the return walk. Descend to a cairn where the track is joined by the one from Corn Du which zigzags down from above the lake. Continue down on the crest of a spur which divides the valley into two in its upper reaches, gaining a good view of the northern end of Cwm Llwch and the agricultural areas to the north.
On reaching the hill fence, cross it by a stile alongside which is a National Trust sign for the Brecon Beacons. This is where the ascent route left the main path and crossed to the stream earlier in the walk and it is now easy to retrace your steps back to the start.
GLACIAL ORIGINS OF LLYN CWM LLWCH
Llyn Cwm Llwch is a small oligotropic corrie lake having a surprisingly shallow maximum depth of only 8m. At a first glance, Llyn Cwm Llwch appears to have been formed by glacial ice sculpting out a deep basin in solid rock but a closer inspection reveals this is not the case. The shallowness of the lake and the hummocky mounds which surround it are the clues to its origins. The lake is situated at the head of Cwm Llwch in a spot which receives the most shade from the sun. Here, one of the last remaining blocks of ice from the Ice Age lingered on. Rock fragments were plucked from the Brownstone crags above by freeze-thaw, a process where water in fissures in the rock freezes, expands, cracking the rock and then melts, penetrating the rock even further before refreezing. These fragments tumbled over the wasting ice mass to accumulate in a ring around its edges. When the ice finally melted, a small lake dammed by the ring of moraine was left. This process is the same as in the formation of ‘kettle-holes,’ of which a fine example can be found beneath Craig Cerrig-gleisiad.
WALK 4
Cwm Sere and Cefn Cwm Llwch
| Start | Pont y Caniedydd (SO 039 244) |
| Distance | 9.5km (6 miles) |
| Total Ascent | 560m (1841ft) |
| Map | OL12 Western Area |
This is a fulfilling mountain route that explores one of the most spectacular and wildest valleys in the Beacons and includes sections which can be demanding in snow and ice conditions. The lower reaches of the valley are well wooded and lead into an amphitheatre created by the steep northern slopes of Cribyn and Pen y Fan. A mountain stream with small waterfalls forms a foreground to Cribyn and Pen y Fan – the two highest peaks in the Beacons. The upper parts of the route can be quite serious in bad or winter conditions but a number of less demanding variations are possible. The main features of interest are the geomorphology and glaciology, the panoramic views and some archaeological sites.
From the car parking area at Pont y Caniedydd, cross the bridge and head south up the tarmac road, passing a farm (Bailea) on the way. On the right of the road in Cwm Sere is a woodland nature reserve managed by the Brecknock Wildlife Trust (see ‘Cwm Sere woodland,’ Walk 7). At the head of this valley is the north-east face of Pen y Fan and to its left is Bryn Teg ridge.
Continue on past the turning on the left to Bailea Farm and follow the road up the hill to where it swings sharp left and through a gate. Ignore this turning and follow the stony track for 250m straight ahead to a gate in the hill fence on the far side of which is a National Trust sign for Cwm Cynwyn. The ridge on the right is the descent route leading towards the end of the walk.
The stony track you have just walked along is part of the Roman Road that leads to Bwlch ar y Fan (see Walk 11). The Scots pines (Pinus Sylvestris) immediately on the left as you cross the hill fence may have been planted as route indicators to drovers and, if this is the case, would have signalled that shelter and grazing could be obtained from the farm nearby. The Roman Road was probably used long before the Romans or even the Celts came to the Brecon Beacons.
Bear right at the gate and follow the stone wall around the front of Bryn Teg and into the valley of Cwm Sere. After about 400m the stone wall has collapsed (SN033 234) Just after this point drop gradually across the slope until the stream course is reached. Follow the stream course, either by scrambling along the bank or by staying on more even ground above, following a convenient sheep track.
Nant Sere
Once in the basin below Cribyn, strike across towards the foot of the north-east face of Pen y Fan and from here climb the headwall by the track which starts from bottom right and continues to top left. You will cross piles of stones brought down the gullies by the winter frosts. The headwall track rises at an easy angle, presenting no problems, and arrives at the unnamed col between Cribyn and Pen y Fan. There is a good view of Cribyn during the ascent.
From the col, climb steadily (W) following the line of Craig Cwm Sere to the summit of Pen y Fan. In early spring the vibrant colours of rare arctic-alpines may be seen on the most inaccessible crags.
FLORA OF NORTH-EAST FACE OF PEN Y FAN
This steep, impregnable 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 which bring the otherwise bleak and foreboding crags alive with vibrant colour in spring. Interesting plants include roseroot (Sedum rosea), rock stonecrop (Sedum forsteranum), mossy saxifrage (Saxifraga hypnoides), purple saxifrage (Saxifraga oppositifolia), vernal sandwort (Minuartia verna), sea campion (Silena maritima), Wilson’s filmy fern (Hymenophyllum wilsonii), globe flower (Trollius europaeus), serrated wintergreen, green spleenwort (Asplenium viride), lesser meadow rue (Thalictrum minus), brittle bladder-fern (Cystopteris fragilis) and northern bedstraw (Galium boreale). These ledges also support an unusual collection of bryophytes and several upland invertebrate species, including a rare arctic aphid. These plants and animals are highly specialised to be able to survive in these extreme conditions.
Looking back down Cwm Sere from the approach to Pen y Fan, there is an ideal view of its geomorphology. Cwm Sere was carved by ice into a
