To the Welsh, the Otherworld was Annwn, also a land of youth and plenty. Annwn was ruled by Arawn or Gwynn ap Nudd, equivalent to the Irish Nuada. Annwn was said to be accessible only through death or through a single door accessible one day a year, located at Glastonbury Tor.

The chief treasure of Annwn was its cauldron, which overflowed with an abundance of plenty, an object similar to the Irish Cauldron of Plenty. One of the earliest Arthurian tales, “The Spoils of Annwn,” concerns a fateful quest for the cauldron, from which only seven men return.

The Welsh story of Annwn was probably the genesis of the Arthurian legend of Avalon, and the cauldron appears to be an early pagan version of the tale of the Holy Grail. Christians seem to have some difficulty with the concepts of the Otherworld, as many tales attempt to reconcile belief in the old pagan concepts of the afterlife. In one Christianized tale of Annwn, Gwyn ap Nudd is given dominion over the demons in order to prevent them from overtaking the earth.

Annwn came to be called Avalon, the name by which the Otherworld is most commonly known today. The name Avalon is believed to derive from the Welsh Ynys Afallach, “Isle of Apples,” a reference to the abundant fruit of the Otherworld. According to Arthurian legends, Avalon was both a place of healing and the final resting place of the king. Strangely, Arthur is accompanied to his final rest by his treacherous sister Morgan le Fey — who may be a version of the Morrigan, the Celtic goddess of death — a fitting escort for a king who ends his life in battle. Arthur was first connected to Avalon by twelfth century chronicler Geoffrey of Monmouth, who also identified it as the birthplace of Arthur's magical sword Excalibur.