Avalon
An alternative name for Avalon, used by Malory and in modern times by Tennyson, who calls it ‘the island-valley of Avilion’.
The idea that it was a valley is found in both Malory and Ralph Higden’s Polychronicon (fourteenth century).
See also
Avaron | The Legend of King Arthur
Source
Le Morte Darthur | Sir Thomas Malory, 1469-1470