Visited 28 August 2010, on a brilliantly clear day. After leaving Nant Tarthwynni, my route headed southwest up to the summit of the little-visited Allt Lwyd ("Grey Hill"), the easternmost of the peaks of the main E-W Brecon Beacons chain. Sadly no summit cairn here, except an extremely paltry modern effort, but there are grand views taking in the whole of the western profile of the Black Mountains range to the northeast. Waun Rydd, flat-topped near neighbour, looms to the northwest. The beehive cairn of Carn Pica can be seen as a pimple on the skyline.
My route heads across to Waun Rydd, up a deceptively tiring (in the heat anyway) incline onto the flat, peaty plateau of the mountain top. Rather than heading to the summit, I cross the rather trackless southern edge of the plateau, above the steep-sided Blaen y Glyn, which involves various diversions around eroded peat hags and boggy areas. The next objective, Bwlch y Ddwyallt ("Two Hills Col") is an odd summit and proves to be incredibly windy. As the name suggests, it feels more like a saddle than a summit in its own right, but there is no denying the spectacular high-level view it gives of Corn Du, Pen y Fan and Cribyn, the central peaks of the Brecon Beacons. Looking north over the lip, Cwm Oergwm drops away towards the lush farmland of the Usk valley.
Feeling sufficiently wind-blasted, I head back towards Waun Rydd ("Free Moorland"), this time making for the summit. From here the Radnor peaks that I stumbled across a week earlier are visible, mist and rain free for once. Following a rough path south and then eastwards from the undistinguished summit, eventually the distinctive beehive cairn appears ahead.
Whatever the authenticity of the cairn itself, the situation is breathtaking. The plateau ends at the cairn and the land drops away below it, down the Tarthwynni valley to the Talybont Reservoir over 500m below. The whole of the Black Mountains profile is visible, down to Pen-y-Fal (the Sugarloaf) and Blorenge. It's a classic bronze age cairn position, placed to command extensive views over the land below, as well as the headwaters of the Tarthwynni brook . If the original cairn was set back a little from the lip, it would be less visible from below, also a common theme with these upland cairns. What a superb spot!
Eventually I tear myself away, straight over the edge onto the steep hillside below. The gradient gradually reduces, heading down onto the broad ridge of Twyn Du. There is a nice overview of the two Nant Tarthwynni enclosures across the valley to the south.
The path finally meets a narrow lane that heads down to Aber Village, and from there I walk back to Talybont-on-Usk, where there are shops, a pub and bus services. A long and tiring walk, but highly recommended on a clear day. The views will blow you away.
The eastern prow of Waun Rydd, a vast moorland plateau rising to a very healthy 2,522ft, is currently adorned by a recently restored (see photo) cairn of a magnitude way in excess of that required for a mere 'walker's cairn'. Perhaps the most likely explanation for this apparent eccentricity is that its original incarnation superseded - for whatever reason, now lost in the mists of time - a Bronze Age burial cairn which once stood here upon this exposed mountain top.
Indeed, according to a 'Field Monuments in the National Park' pamphlet, published by the Brecon Beacons National Park Committee in 1983, "... a few paces to the west... [of the existing cairn]... are the mutilated remains of a probable prehistoric burial cairn, much of it having been destroyed by generations of passing walkers" (suffice to say that 'walkers' is not a term I'd use!) This assertion is supported by the local Clwyd-Powys Archaeological Trust, not to mention the name 'Carn Pica' itself. Seems pretty solid reasoning to me.
It has to be said that very little of the original cairn remains, but - by all accounts - the site is authentic, the views sublime, the vibe likewise. Well worth a visit.
If the thought appeals, Carn Pica is perhaps best reached by a somewhat arduous walk/climb from Tal y Bont Reservoir, via the Twyn Du ridge. Map, compass and waterproofs essential.