Cantre’r Gwaelod, also known as Cantref Gwaelod or Cantref y Gwaelod (English: The Lowland Hundred), is a legendary ancient sunken kingdom said to have occupied a tract of fertile land lying between Ramsey Island and Bardsey Island in what is now Cardigan Bay to the west of Wales. It has been described as a “Welsh Atlantis” and has featured in folklore, literature and song.
Source: Cantre’r Gwaelod – Wikipedia
Tim B.
https://en.wikipedia.org/wiki/Llys_Helig
“Rachel Bromwich discusses what she refers to as the folk-tale of Cantre’r Gwaelod, another alleged sunken kingdom but in Cardiganshire. As with Llys Helig, there are tales of remains being seen of the sunken kingdom. Bromwich believes that the two stories influenced each other, and that “The widespread parallels to this inundation theme would suggest that the two stories are in fact one in origin, and were localized separately in Cardiganshire and in the Conway estuary, around two traditional figures of the sixth century. She also notes that the Halliwell Manuscript gives Helig the title “Lord of Cantre’r Gwaelod”.[5] In the book New Directions In Celtic Studies Antone Minard wrote that “The Welsh legends of Cantre’r Gwaelod and Llys Helig (Helig’s Court) contain the same details of audible bells beneath the waves and ruins which are visible at the equinoctial tides, which are the anchors of credulity in the story”.[6] “