A better translation of Go Rin No Sho is "Book of Five Spheres" since in Buddhist literature the Five Spheres were the four appendages of the human body, and the head. Historically, it's generally agreed that he was a damn good artist and sculptor as well. It's also commonly believed that he was the greatest sword fencer in Japan ever, and it's true that every book on Kendo has his book in its bibliography, but Masaaki Hatsumi has gone on record as saying that there were many swordsmen who were as good or better, it's just that Musashi wrote it down.