https://www.bbc.co.uk/news/uk-wales-62605682
This BBC story about sunken islands revealed on a medieval map is interesting. (in the light of the story in the Black Book of Carmarthen)
Though I think that the quotations from Juliette Wood rather blur the distinctions between myth, legend and folklore.
awenydd.cymru 
Yes – saw that. I wonder what else will come to light…