Valley just north of the highest summits in Brecon Beacons National Park, containing a stream (Nant Cwm Llwch) that originates from a secluded lake, and flows over a sequence of waterfalls. Viewed along a hike that also visits a memorial obelisk, on the ridge leading to the peaks
Cwm Llwch is a valley at the north edge of the Brecon Beacons, just below the two highest peaks in the range, Corn Du and Pen y Fan, and it provides an alternative hiking route to these summits, much less travelled the main approach from the west, starting near the Storey Arms along the A470. The distance to Pen y Fan is about the same, a little over 2 miles, though the elevation gain is somewhat more, 2,000 feet compared to 1,500 feet.
Besides the much quieter surroundings and the grand views of the north side of the peaks, the valley is also notable for a series of waterfalls along the stream that flows down (Nant Cwm Llwch), a small drainage though one that usually carries enough water to create some impressive cascades, flanked by isolated trees and layered rocks covered by rich green vegetation. The stream originates from a small, secluded, glacial lake, Lyn Cwm Llwch, one of only three significant (natural) lakes in Brecon Beacons National Park, the others, much larger, being Llyn y Fan Fawr and Llyn y Fan Fach. The lake has a scenic setting beneath steep, layered, reddish slopes, and while it can be seen from afar along the main route to Pen y Fan, much better is to approach close up.
The path stays between 200 and 1,000 feet from the upper portion of the stream (which splits into two branches), so to see the waterfalls properly requires an off-trail diversion, and some scrambling up steep, sometimes slippery slopes. The round trip to the obelisk is 4.2 miles, to Corn Du 5 miles and to Pen y Fan 5.8 miles. One other point of interest along the Cwm Llwch trail, on the ridge extending north from Corn Du, is an obelisk, erected in 1900 in memory of Tommy Jones, a 5 year old boy who became lost when climbing the valley at night. In addition, as well as the waterfalls in the upper reaches of the valley, close to the trail, the Nant Cwm Llwch forms other falls lower down; some are not so accessible, hidden by dense woodland, but two (Rhyd-goch and Ffrwd-grech), either side of a bridge along the approach road, are easily seen, and well worth a quick stop.
The hike up Cwm Llwch starts from a small parking area, not signposted, at the end of a narrow lane (Ffrwdgrech Road) 3.8 miles south of Brecon - the road passes under the A40, continuing straight on at a three-way junction, then past three other minor intersections to a gate, where it becomes unpaved. Parking (and camping) is in a field on the far side, from where a track continues another half a mile to the old Cwm Llwch farmhouse, now occasionally used as a hostel, for Malvern College; the trail starts on the far side. The farm was the destination for Tommy Jones in 1900 but he became separated from his elder brother just a quarter of a mile back at another house, the now ruined Login, and must have wandered on some distance up the valley. His remains were only found 29 days later.
Ffrwdgrech Road crosses the Nant Cwm Llwch 1.4 miles from Brecon, and stays close to the stream all the way until the end. The bridge is in a narrow wooded valley, and either side of the crossing are two waterfalls, both easily viewed along short paths. Downstream of the bridge is the Ffrwd-grech waterfall, where the creek tumbles about 15 feet over dark cliffs into a pool, followed by a smaller cascade and a larger pool, while upstream, a slightly longer walk leads to a similarly-sized fall, perhaps named Rhyd-goch after a nearby dwelling. These falls are a little more photogenic, as the stream drops in stages into a briefly enclosed channel, bordered on the southeast side by cliffs from an old quarry.
The walk from the parking area is along a continuation of the vehicle track, through sparse woodland, over the stream on a footbridge, round the Cwm Llwch hostel and out to an open, grassy ridge, climbing steadily though not to steeply. The trees quickly fade away allowing uninterrupted views across the valley, to the two high spurs at either side (Pen Milan, Cefn Cwm-llwch), and the twin summits of Corn Du and Pen y Fan to the south. The stream is visible below, flowing through a V-shaped gulley, which divides after half a mile from the hostel. Both branches have several waterfalls, the best being along the east fork, approached by descending to the confluence then walking up beside the streambed. The first, and tallest, is a two stage drop, partly hidden behind a few large trees, where the stream flows over layered cliffs partly covered with much green vegetation, then above is a sequence of lesser falls, mostly lacking any trees. The west branch of the stream has a few small falls at the lower end, including one attractively framed between a pair of wind-blown trees, and a pretty sequence of three closely-spaced cascades
Above the waterfalls, the land is less steep, the drainages become shallow, and it is easy to walk cross-country back towards the path, which steepens somewhat as it approaches Llyn Cwm-llwch. The lake itself is not especially remarkable, about 2 acres in size, filled with dark, tannin-stained water and ringed by grassy mounds, but it has a dramatic setting beneath high slopes on three sides, some parts of which are red due to exposures of the Old Red Sandstone that make up most of the Brecon Beacons. The path swings west, winding steeply up to the rim of the plateau, then cuts back southeast, ascending more gently up a broad spur that leads to Corn Du. The Tommy Jones obelisk is directly above the lake, next to a seasonal pond.