Traditionally, the earliest Christian sanctuary in Britain. Glastonbury Abbey was a rich and powerful monastery in Glastonbury, Somerset, England. Since at least the 12th century the Glastonbury area was frequently associated with the legend of King Arthur, a connection promoted by medieval monks who asserted that Glastonbury was Avalon. History records it as standing in 600. Really mythical, powerful feel to this whole area. Not to be missed. Orange Filter.