Merlin’s Hill, Abergwili.
The end or final fate of Merlin is surrounded by mysteries. A few years ago when I was staying n the neighbourhood of Carmarthen, Merlin’s Hill (Bryn Myrddin) was pointed out to me where the great magician still lives (so they say) in a cave in that hill, and held there in imprisonment by an artful woman who contrived his disappearance from among human beings. Moreover, it is added, that if you listen in the twilight, you will hear his groans, and also the clanking of the iron chains which hold him bound. Others say he is heard working in this underground prison.
From ‘Folklore of West and Mid-Wales’ by J C Davies (1911).