Fan y Big from the Upper Neuadd Reservoir

Fan y Big is the lowest of the four summits on the Beacons horseshoe, at 719m by the figure Visit Wales and the Ramblers both give, and the one with the rock known as the diving board. The Neuadd valley is the quieter way in. Fforest Fawr Geopark records that the Upper Neuadd Reservoir was built between 1896 and 1902, with limestone brought in on the temporary railway from Torpantau halt that had served the Lower Neuadd dam of 1884, and that at 459m above sea level it is the highest reservoir in the national park. Talybont-on-Usk is the nearest base, and the National Trust directs drivers from the village along the reservoir road and up a steep wooded hill to the second Forestry Commission car park.

Walking Britain starts its four-summit round at SO 035 173, from where a lane runs north to the Filter House and across the abandoned dam wall. A steep path reaches the edge beside the 642m trig point, and the escarpment carries the route over Graig Fan Ddu to Corn Du, Pen y Fan at 886m and Cribyn. At Bwlch ar y Fan, the gap beyond Cribyn, the National Trust describes the Gap road as the first track to carry horse-drawn carriages over the range, thought to be Roman though no archaeological evidence has been found. Walking Britain offers it as the way back to the car park for anyone out of energy, and counts the climb on to Fan y Big, about 120m, as the last major ascent of the day. From the summit the Beacons Way follows the edge south and drops east of Craig y Fan Ddu to the forest.

Walking Britain gives the full circuit as 17.4km with 848m of ascent, grading it moderate to hard; the Ramblers and Visit Wales give the horseshoe as 16km, graded challenging and hard. The National Trust advises a map and compass, waterproofs, a whistle and a torch, welcomes dogs on leads, and calls parking limited.

The round suits a walker with a full day, a tolerance for steep descents and a map they can read. It is not a walk for anyone short of daylight or for children who tire quickly, because Walking Britain describes steep ascents and descents between the summits. Pen y Fan from Pont ar Daf reaches the highest of them in 6.4km and about 450m of ascent.