I say hidden as books in English on traditional Japanese hot springs (onsens) are rare. Neff is a real traditioalist at heart and refuses to recommend any onsen that has tried to fit in with the modern city-driven development of Japan. His enthusiasm for finding peaceful, beautiful locations, with onsens set in natural locations knows no bounds! Locations given in the book live up to their expectations. This is certainly the best onsen guide showing a side of Japan that has resisted change, and will hopefully continue to do so - see it before it does!