Also known as the Sunken Forest, Cantre'r Gwaelod is the subject of one of Wales's best-known folk tales. The legend says it is the gate to a former fertile land of 16 cities that are now covered by the sea in the Cardigan Bay. The legend has inspired many poems and songs. It is thought that the story came to be because of flooding that happened in the area between 17,000 and 7,000 years ago due to Ice caps melting in northern Europe and North America. The stories of this flooding were passed down from generation to generation, eventually becoming folklore. Cantre's Gwaelod is referenced in Finch's Real Wales: "Wales, the invisible, the lost. Wales, the real Cantre'r Gwaelod. A small island in the Hebrides. A rock off the west coast of Ireland. A hummock out there in the stormy ocean. Wales, Grassholm writ just that little bit larger. Floating west, full of birds." Finch talks here about Wales being forgotten or largely unknown to the rest of the world for what it truly is. Drawing parallels to the story of the lost land of Cantre'r Gwaelod by calling Wales the real Cantre'r Gwaelod.
Sources: https://www.bbc.co.uk/legacies/myths_legends/wales/w_mid/article_4.shtm…