Foel Cwm-Sian-Lwyd, rising to 2,125ft, crowns the north-eastern apex of a considerable expanse of (deceptively) desolate, heather-clad moorland set between the main ridge of Y Berwyn to the east, across Cwm Pydew, and The Arans to the west, the latter rising beyond neighbouring summits sometimes referred to in the collective as 'The Hirnants'.
The summit ridge bears the remains of (at least) two cairns, although only that to the north is cited as having probable prehistoric ancestry by Coflein. Although that would be more than enough to encourage a visit in itself... I disagree, my experience strongly suggesting - to me, at least - the summit cairn is also an apparently unopened burial cairn, albeit badly disturbed by the subsequent erecting of an OS trig station. Ironically, it appears the OS agree with me.
The cairn sited upon the northern prow of the mountain (SH99713172) is a large construction measuring 'about 15m in diameter and up to 1.5m in height on its N. side' (according to Coflein), sadly surmounted by a substantially rectangular dry stone construction which, bearing in mind the surfeit of heather, may well be a shooting butt. If so it shows, if my perception is anything to go by, signs of having been rebuilt at least once in it's lifetime. Three is a nice, rounded number too, don't you think? Needless to say, despite the pretty severe wind and lashing showers, I refuse to enter on principle, namely that one has to dress for the occasion, whether that be a night in a posh restaurant or an afternoon watching rainbows arc above Cadair Berwyn. And not lower one's standards.... Whatever, it must be said that the grassy footprint is pretty impressive and this is a good place to be, the scenery illuminated with vibrant colours from cobalt blue to the most orangey of orange - and pretty much everything in between - during periodic sunbursts providing brief hiatuses from swiftly advancing storm fronts riding the prevailing wind.
The summit cairn (SH996314), by contrast, has a somewhat lower profile but nevertheless the footprint is convincingly 'authentic' to these eyes, bearing comparison with the not-too-distant Bronze Age cairn of Foel y Geifr. Furthermore, by my reckoning it's pretty certain that this was not erected by walkers in this more-or-less unfrequented part of Wales. Although, to be fair, the summit of Foel Cwm-Sian-Lwyd possesses views that rival many a more popular mountain, encompassing not only the Berwyn and Aran heights, but also the Arenig, Clwydian, Cadair Idris.... and much else besides, stretching all the way to northern Snowdonia.
There is a downside, however. Despite appearances upon the map and, indeed, from the B4391, there is no 'easy' route to the summit of this mountain. So be warned. In fact 'masochistic purgatory' might be a more apt description of even the short ascent from the obvious parking area near the sharp U-bend at Pont Cwm Pydew. Trackless heather is like that. But there are compensations, shall we say?