Originally, Annwn was said to lie so far to the west that not even Manawyddan ap Llyr had found it, for you could only reach Annwn by dying yourself. Later, however, it was said that Annwn could be entered by those still living, near Lundy Island and Glastonbury Tor. St. Collen, a Welsh saint, entered Gwynn's palace to banish him with holy water.
In the Book of Taleisin is a 10th century poem called The Spoils of Annwn. It is about King Arthur and his knights traveling through Annwn, searching for a magical cauldron possessed by nine women. Only seven knights survive the journey. It may be a precursor of later Holy Grail stories involving King Arthur and his knights. The nine maidens related to actual groups of nine priestesses in ancient Celtic society. Geoffrey of Monmouth told stories of Morgan le Fay and eight other priestesses in his poem, Vita Merlini, who lived on the Isle of Apples or Avalon. Avalon was often identified with Annwn.