It occurs to me that “Onhava” is a near-anagram, or one word-golf move, of “Avalon”, the mystical Isle of Arthurian legend.
Avalon was the home of Merlin and Morgan La Fay – a misty land of enchantment.
I am not terribly familiar with the Arthurian lore, but the sword in the stone and the grail legend fit the “Hero’s Journey” quest that is suggested in Pale Fire. There seem to be other parallels, e.g. Hazel and “The Lady of the Lake”.