In the interests of possibly outcroppy places with stoney folklore I am compelled to add this curious feature. (No, I do admit I've no proof it has prechristian significance.) Someone went to a lot of effort to turn this boulder into a not terribly comfy-looking chair, and it must have been done some time ago as it was apparently mentioned in a 15th century poem by Hywel Rheinallt. I can't find anything about it online and still less a photo, but it's on modern maps and I think I can even see it on satellite photos.
The writer in the 1856 'Archaeologia Cambrensis' says:
On a small eminence, a quarter of a mile eastward from the church, is a large boulder stone, with a flat piece cut out of it, called Cadair Cawrdaf, -- St. Cawrdaf's Chair, from time immemorial. Judging from the site, the saint must have been a lover of the picturesque, for the view is one of extreme beauty and extent.
The church in Abererch is dedicated to Saint Cawrdaf, and not far away northwest, at SH38823735, is his spring, Ffynnon Cawrdaf.