Kevin meets a master craftsman whose dream is to build a castle made entirely of mud. Kevin McCabe is the leading living exponent of the ancient art of cob building - wrestling houses out of mud using his bare hands. But Kevin doesn't just want to build another cob house, he wants to build a cob castle. Not only that, Kevin also wants their gigantic new cob house to meet the highest environmental performance targets ever set. It is truly an almighty challenge. The house will be formed of two vast curved cob roundhouses - the largest of which is inspired by the natural geometry of a snail shell - connected by glazing and topped with undulating wild-flower meadow roofs to mirror the surrounding Devon countryside. But building it involves mixing and laying a mind boggling 2000 tonnes of cob, all during warm sunny weather. Kevin is determined to have the main cob walls up in a few months. But soon the sheer scale of the task becomes clear.