I was brought up on the Lleyn Peninsula in the 1950s / 60s and was taught a poem at school called Clychau Cantre Gwaelod (the bells of the hundred on the bottom). It was, as I recall, about a lock keeper called Seithenhin who lived in low lying land in Cardigan Bay. He fell in love with a beautiful princess and left his post to be with her. I think she spurned his advances and he got drunk. He left the sea gates open on a night when there was an on-shore wind and high tide. The sea inundated the walled village. He and the princess drowned and it is said that the bells of the submerged church can be heard under the sea, proclaiming the loss of the princess and the community. There is a similar legend concerning Caer Arianrhod, in Caernarfon Bay, between Dinas Dinlle and Pontllyfni but the poem almost certainly relates to Cardigan Bay. Hope this sparks more debate!