I just spent a week in Central Honshu. Jigokudani Snow Monkey Park (the place where you can see Japanese macaques in hot springs) was virtually unknown when I first visited in 2005, but now it’s very touristy. Try visiting just before closing time (you have to be at the parking lot at 16:00) to avoid the crowds; that also maximizes your chances of seeing serows on the way back (we saw one). Kose Rindo track in Karuizawa (trailhead at 36.363757N 138.591144E) had lots of animal tracks before dawn, even though the snow kept falling all night: martens, Japanese weasels, foxes, sika deer, serows, Japanese hares, and non-feral black rats. I tracked down one hare and also saw a black rat and a Japanese field vole, plus a Japanese flying squirrel on one of nestboxes put up for Japanese giant flying squirrels, and also two Japanese squirrels after sunrise. Spent a night at the Japanese water shrew site at 35.4625N 139.267202E; didn’t see any shrews but found a lesser Japanese mouse and a Smith’s red-backed vole, plus a few small rodents I couldn’t identify.