Katherine Derbyshire and I went to see it last night. I hadn't realized it is the family collection of the Hosokawa family, for whom Musashi had been sword instructor, so that much of his work has been in that family for centuries. There is no extant version of the Book of Five Rings in his own hand, but this has the best thing available: five scrolls transcribed by Terao Katsunobu contemporaneously and the earliest known copy. Each of the 5 scrolls is open for viewing. It totally knocked us out that they let them travel. Such a wonderful thing to see.
In San Francisco through Sept 20