Glastonbury is famous for being one of the most mystical sites in the world. It has connections with King Arthur (the Arthurian legend), Joseph of Arimathea, Glastonbury Tor, The Abbey, the Glastonbury Giants or Zodiac, the intersection of Ley Lines and Earth Energy Lines. Glastonbury is also believed to be the mythical place known in Arthurian Lore as 'The Isle of Avalon'.
In Twin Peaks, Glastonbury Grove is first seen at the end of episode 27. Not until the final episode of the series, episode 29, was the place actually called by name, Glastonbury Grove by Agent Cooper.
According to the original shooting scripts the spelling was Glastonbury but later publications written by the same writers (Lynch, Frost and others) had a different spelling, Glastonberry. The reason for the change was never given but it has been thought that the change in spelling was provided as reference to the pies, the notable berry pies Norma Jennings could bake at the Double-R Diner.