http://www.caer.co.uk/carving.htm
shows the supposed carving of a man and serpent , found on the inside of a Cornish Fogou.
The article on the webpage is an extract from 'Fogou - A Journey into the Underworld' by Jo May.
Phil
have you finished the book? I've got half-way through, but threw it across the room in disgust at yet another speculative historical reconstruction ...