In 1809, the Gough map at the Bodleian library in Oxford would reveal a bizarre secret: the existence of two small, mysterious islands off of the coast of Ceredigion in Wales.

What made these islands stand out, though, was the fact that they no longer existed. There were no islands in this portion of Ceredigion Bay, and according to the maps known to historians today, there hadn't been islands here since at least the 1600s.

To add even more fuel to this mystery, these islands appear to have existed precisely where a Welsh legend of a medieval kingdom that sank into the ocean took place.

What started as a question on the existence of two missing islands, developed into a mystery of whether or not this ancient story of a sunken kingdom was actually based in reality. In this video, we will examine whether this medieval mystery really took place in the history of Wales.