The myth of the grail provides the title for this book about the possibility of perception beyond the physical world. The occult and the invisible are objects for the imagination, which in the Middle Ages was seen as a visionary experience granted by God. The first chapter opens to a vision based on a confrontation between an older culture, with a mystic such as H. von Bingen, and a more modern one. Chapter 2 explores techniques for opening the inner eye, presenting a conversation between Cervantes and Leonardo da Vinci or Breton. Chapter 3 analyses feelings towards nature from medieval mysticism and bohemianism to romanticism and Caillois. Chapter 4 looks at the place of the visionary, from the Abbot of St. Denis to Picasso. Part 5 studies the myth of the Holy Grail and 6 deals with visionary figurativism as compared to the geometric.