For various reasons, Somerset and Arthurian history, myth and legend come hand in hand. It is known that once in that area of what is now called England reigned a post-roman King known as Pendragon(with many different spellings according to whatever source mentions him), who may or may not be a mythological individual, but it really ties down the legend with that geographical location. Then, of course, there is Glastonbury and Glastonbury Tor, which many people believe to be the site commonly known as the Island of Avalon in Arthurian Legend.
It is not known if its construction was done before or after the Arthurian legends supposedly took place, but there is a spiral labyrinth in Glastonbury Tor that has the visitor take several turns around the hill to reach the top. This was often the physical representation of a spiritual journey for ancient cultures, and it seems to reinforce the idea that Glastonbury Tor may not have been Avalon itself, but a doorway to Avalon, which according to myth does not exist in the physical plane, instead being an ethereal place.
If you want to see this up close, pay a visit to any Somerset car hire company, drive down and experience it for yourself.