Nobody goes right: Bronze Age cairns on the Black Mountain
Distance and ascent computed from the recorded GPX track (ascent at a 3 m smoothing threshold). The western half is pathless and on limestone; the difficulty reflects the navigation, not the terrain underfoot.
The story
Everybody who parks at Llyn y Fan Fach goes left. Left takes you along the escarpment to Picws Du and Fan Brycheiniog: big views, a well-worn path, four hours, home for tea. It is a brilliant walk. I have done it.
This route goes right. West off the escarpment, onto Carreg yr Ogof and Garreg Las, where there is no path and almost nobody goes. The ground changes under your feet: sandstone gives way to limestone, streams vanish, and the moor is pocked with shakeholes where the surface has collapsed into whatever is underneath. You camp between two Bronze Age burial cairns, each fifteen metres across, that someone dragged into existence by hand four thousand years ago on the highest ground they could find.
Two days, one night, and I saw two people the entire time. Both of them were going the other way.
The wall at the end of the lake
The lake is natural. The ice carved this north-facing hollow and left it here. But the wall at the far end is not: somebody built it for a town twenty-three miles away that you cannot see from where you are standing.
Llanelli. The tinplate industry had made that town rich and filthy at the same time. It grew faster than its own drains, and what came out of the taps was not fit to drink. So they went looking for somewhere clean and high and empty, and they picked this. Act of Parliament, 1912. Work started in 1914, with about a hundred and seventy-five Irish navvies living in two wooden huts roughly where the car park is now.
And then the war started taking them.
By 1916 they could not keep anyone up here. So the council asked the War Office for prisoners of war. They were told no. Instead they got conscientious objectors: men who had been called up and refused, would not sign the papers, would not put the uniform on. Most of them had gone to prison for it. There was a Home Office scheme that let them out of prison on condition they did hard labour instead. Llanddeusant was one of only four such camps in the whole of Wales.
About two hundred of them came through over the years, mostly from Manchester and Birmingham and the Midlands, out of Cardiff and Llanelli prisons and up here. Living in the huts the Irishmen had left. And when the war ended, they were not let go. They were kept on so the soldiers coming home got first pick of the work.
The dam is a Grade II listed building now. Cadw listed it specifically for that association. There is a date carved into the keystone of the outlet tunnel: 1920.
Where the water goes
Once you leave the escarpment and head west, the geology changes and you can see it. The Old Red Sandstone gives way to Carboniferous limestone, and limestone leaks. The streams disappear. The rain does not run off; it goes down, into a karst landscape of shakeholes and collapsed hollows where the surface has slumped into what is underneath.
Carreg yr Ogof, the next summit along, means "rock of the cave". And there is one: a thirty-seven-metre hole on the north side, under an old limekiln, with two chambers, a squeeze, and a green pool at the far end that divers have already been down to find it does not go anywhere. A whole mountain, named after that.
But the wider system goes a long way. From the sinks a few miles south, the water has been traced: four miles of underground travelling, three hundred metres of drop, and it takes a week. It emerges from a cave called Llygad Llwchwr, the Eye of the Loughor. That is where the River Loughor starts, out of a hole in a hillside.
This is also why you carry water. Everything on the limestone side is dry; the last reliable source is below the dam. Four litres on your back is the price of camping up here, and it is not enjoyable on the climb.
Four thousand years old
The camp sits between Carnau'r Garreg Las: two enormous Bronze Age burial cairns, each about fifteen metres across, the northern one up to two metres high and the southern nearly two and a half with a robbed hollow in the centre. They are scheduled ancient monuments, dated by analogy to roughly 2000 BC. Neither has been excavated.
But the cairn on Fan Foel, the spur at the far end of the escarpment behind you, has. Dyfed Archaeological Trust dug into it in 2004. Inside they found a stone cist about a metre long, and in it the cremated remains of an adult, a child, and an infant. They also found pollen: meadowsweet, unburnt, both bud and full bloom. It had not gone on the fire with them. It might have been flowers, laid in afterwards. It might have been a drink, sweetened and flavoured, placed in the pot for them. The archaeologists and the literature still argue about which.
Either way, somebody stood up here four thousand years ago and brought something for the dead. That is not just a burial. That is a funeral.
The walking
The route starts from Llanddeusant, at the north-west corner of the Black Mountain (that is the Black Mountain singular, Y Mynydd Du, not the Black Mountains plural near Hay). You walk south-east through lanes and fields to the Llyn y Fan Fach car park, then up past the lake and the dam to the escarpment via the zigzag path. From the top of the zigzags, the standard route turns left along the ridge. You turn right.
From here there is no path. You cross a col at about 540 m where the geology changes, then climb onto Carreg yr Ogof (585 m) and along to Garreg Las (635 m), where the cairns are and where you camp. Navigation on this section is compass-and-pacing ground in poor visibility: the moor is broad, featureless, and pocked with shakeholes that are a genuine hazard in cloud. Say so to anyone who asks, because it is honest and it is the kind of detail that builds trust with a walking audience.
Day two takes the cave on the north side of Carreg yr Ogof, then descends north into the Tywi valley and loops back to Llanddeusant. The morning light on this descent is the best of the trip: low sun from the east, the valley opening ahead, and nobody around because everybody else finished yesterday afternoon.
The camp
Garreg Las at 635 m on an open ridge. If it is blowing, get in the lee of the northern cairn and accept a tighter frame. The sunset sits behind you to the west-north-west; if the sky is clear, the Milky Way runs south along the ridge after dark, and the Perseids were warming up when I was there in early August.
Wild camping is not a legal right in Wales. This is common land with grazing rights. The usual discipline applies: pitch late, pitch high, keep it small, and be gone by dawn. Leave nothing. Ten honest seconds about this on camera is better than pretending the question does not exist.
Practical notes
Water is the planning constraint. The last reliable source is below the dam at around 4.5 km. Everything west of the escarpment is limestone and runs dry. Carry four to five litres from the sandstone side and plan the camp around where you can carry water to, not where you will find it.
Navigation west of the escarpment is real map-and-compass work in poor visibility. The shakeholes all look the same in cloud and some are deep enough to be a problem. A GPS track helps, but do not rely on it alone.
The cave entrance on Carreg yr Ogof is about 150 m north-north-east of the trig point, below a disused limekiln. It is thirty-seven metres long, two chambers and a pool, and has been fully explored. Do not go in alone, and honestly, do not go in at all without proper caving kit and someone who knows what they are doing.
Bannau Brycheiniog is an International Dark Sky Reserve and you are camping in one of its emptiest corners. If the sky is clear, it is worth staying up for.
Filmed for the Jim's Wild Trails channel. If you walk it, tell me what I missed. Corrections welcome: social@jimswildtrails.online.
Also on this site: Wellington MF509 bomber wreck and wild camp.