The greatest mystery of Glastonbury is the question of whether King Arthur's body was buried on the abbey grounds.

An excerpt from the article 16 facts about Glastonbury

Despite the monks' declarations about the discovery of the remains of the king and his wife Guinevere in 1190, there is still no certainty on this matter. Recent research suggests that the king may have been buried near Bridgeen in south Wales. After the last battle of Camlann, which is a difficult place to identify, the dying king was taken to the mysterious island of Avalon.