Preiddeu (spoils of) Annwn (or Annwfn) is a cryptic poem of sixty lines, found in the book of Taliesin; claimed to be written in Middle Welsh but more than likely written in the Cumbric (now defunct) dialect. This recounts a journey made by King Arthur to Annwn purportedly to raid its spoils and is one of the earliest mentions of King Arthur. Annwn it would seem is referred to by several names, including “Mound or Fairy Fortress,” “Four Peaked or Cornered Fortress,” and “Glass Fortress”.
As the surviving manuscripts all date from the 13th, 14th and 15th C and were scribed by monks we have to be aware of any ‘Christianisation’ of these tales by the scribes.
These Mythologies do however give us a lot of information about the Otherworld – Annwn. Its rulers/Kings; Arawn to start and later Gwyn ap Nudd and other inhabitants were superior beings and not to be trifled with from our world. There are tales of opulent feasts and entertainment for guests that far outweigh anything that can be offered in this world and the impression is given that abilities (magical or not) are well beyond human reach.
Annwn; a land of eternal youth and delights where disease is absent and food ever abundant is the home of Gods & Goddesses and the Fae. Otherworldly creatures and maybe much more reside here as the Brythonic landscape is littered with non-human beings who live in worlds (different realities or realms) other than that in which WE reside.
These non-human beings are to be found in Faerie Stories and folk-lore are associated with magic and astonishing skills/craftsmanship; these are the elves, dwarfs and gnomes to name but a few. The worlds in which they live are never named so that we do not know if it is the same Otherworld or if there are many.