Samuel Firman writes for the BBC:
Set amid the hilly wetlands of the Somerset Levels, Glastonbury has been a spiritual magnet for centuries. In the Middle Ages, many believed that Joseph of Arimathea visited with the Holy Grail, and the sacred cup is central to the Arthurian legends that infuse the town and its landscapes. Glastonbury is also considered the hub of English “Neo-Paganism”, a collection of pre-Christian beliefs and spiritual practices undergoing a modern renaissance, including witchcraft, Wicca, the Goddess movement and Druidry.
If you’d like to go deeper, I recommend the Normal for Glastonbury blog.