Celtic Other World
(the giant Cuchulain)
There is also a story of Arthur making a journey to the Otherworld gained possession of a magic cauldron--a pagan Celtic type of the Holy Grail--which furnishes inexhaustible food though 'it will not boil the food of a coward'.
Our book states, "the prototype of the grail was a Celtic vessel dispensing food and drink in an Otherworld atmosphere of perpetual youth and feasting."