(S/E)To reach the start drive west on the B4601 from Brecon town centre. Turn south on to Ffrwdgrech road at grid ref. SO035283. Take the left fork (grid ref. SO028272) and passing Danyfan on the right, continue a further 0.8 miles to Cwmgwdi car park (grid ref. SO 024248). After parking return to the car park entrance, cross the cattle grid and turn left along the lane. After crossing the bridge over Nant Cwm Llwch river turn left and head south into Cwm Llwch.
(1)Continue on the west side of the river, initially on road then pathway, skirting closely around to the right of Cwm-Llwch farm. The pathway now climbs steeply up the beautiful Cwm Llwch valley, with Pen y Fan and Corn Du coming into view. After crossing a stile into National Trust land a short detour can be made to take a closer look at the picturesque waterfall to the east of the route. Take care on the steep ground adjacent to the watercourse. The main route continues to the right of a small lake (hidden until close) and up to the ridge. Continue past the poignant obelisk in memory of young Tommy Jones (the story is written on the stone) and on to the top of Corn Du. On a clear day you will have commanding views of all the tops of the Beacons.
(2)From Corn Du it is a short distance to the broad summit plateau of Pen y Fan, at 886m the highest peak in the Brecon Beacons and Southern Britain. If a shortened walk is desired you can leave the summit towards the north and return more directly to the beginning of the walk. However, it is well worth continuing to get the best views of Pen y Fan, and to enjoy the less busy tops of Cribyn and Fan y Big.
(3)From the top of Fan y Big return to the saddle between Fan y Big and Cribyn, and take the well-defined track (an old Roman road) northwards, steadily descending along the western side of Cwm Cynwyn. Where the paved road begins take the left route. After crossing the bridge over Nant Sere river, take the second small lane (grid ref. SO040245), then bear right on the footpath across fields to skirt around to the right of Plas-y-gaer farm. Continue through gates to rejoin a lane. Take the next left, then either right to return to Danyfan or left to Cwmgwdi car park.
