This prominent hill seems to maintain its presence in local minds even today: I read on the 'UK Weatherworld' forum "the biggest hill for miles around.. is locally known for being a focal point for thunderstorms! :)". It had a bit of an eerie reputation in the past as the haunt of fairies. The following stories are retold by Janet Bord in her 'Fairy Sites' book (citing Davies's 1911 'Folklore of West and Mid Wales' as her source*).
*I've now substituted Davies's text:
Mr. Edward Jones, Pencwm, who only died about 8 years ago, was coming home from Lampeter one moonlight night, and when he came to the top of Trichrug hill, he saw the Fairies dancing in a field close to the road. When he was within a certain distance of them he felt as if his feet were almost lifted up from the ground, and his body so light that he could almost stand in the air.
My informant, Mr. D. Morgan, Carpenter, Llanrhystid, added that Mr. Jones was an intelligent and educated man, who had travelled, and was far from being superstitious.
The area was once moorland, though now it is a planted forest, so maybe the fairies are harder to find now. It sounds like a plausible account -oh come on, it's all relative - what I'm trying to say is, it sounds more likely to have happened than the next one, which is over complicated and turns into a blatant folktale by the end =
This one concerns a painter and flautist in the 1860s called John Davies. He'd just left the Rhiwlas Arms(!) and was making his way over the moor. He thought he was using a light from a cottage to guide his way, but it turned out to be a fairy light (a willowthewisp for you cynics) and wandered off course into a bog. Early the next day a woman from the actual cottage heard strange music and following it to its source found JD playing his flute. He told her that he'd met a ring of dancing fairies wearing white knee-length dresses, and that he'd played the flute for them. He'd asked the 'fairy queen' for a wife and she'd agreed, saying that they had to return to visit once a month at the full moon. When the woman from the cottage turned up he was just being handed a pot full of gold as well, but at that point all the fairies had just vanished.
Trichrug, a mountain of Cardiganshire, so called from three small mountains being connected with it, was celebrated not only as a place of fairy resort, but as being once the spot where stood the seat of a giant, whose grave (as some say) is still to be seen, and which is described as fitting any one who will lie within it, whether he be tall or short, and that the person so lying in it will have renewed strength; tradition also relates, that if arms are placed therein they will be immediately destroyed. It is said of this giant, that he invited the neighbouring giants to try their strength with him in throwing stones, and that he won victory by throwing his quoit to Ireland! (a pretty good distance to throw a stone!)
From 'Cambrian Superstitions' by W Howells, 1831.
You can see another stone he threw at Llech Bron.