The monkey park was amazing, and this ryokan is almost on top of it. It's so close that a monkey walked along the edge of our outdoor bath, and we saw other monkeys on the roof! There is a natural steam vent on the property (little sulfur smell, but not bad) and a river running through it, and you can see all of this, along with tourists going to see the monkeys, if you are soaking in one of the outdoor baths. The family who runs the ryokan are extremely nice. The mother makes all the food, which was fantastic and had generous portions. Dinner and breakfast the following morning are included. It was about a 20 minute walk from where the taxi dropped us off in the park parking lot, and about 30-40 minutes leisurely walk on the (better paved) path to the bus stop in town. Either way, I was glad to have a backpack and not a rolling suitcase. Korakukan has a very rustic, mountain-lodge feel. It's not fancy, but we loved it and felt it was worth the price (considering how hard it must be to run such a place year-round inside a national park). The listing says check-in is only until 16:30, but we called to tell them we were running late and they didn't mind. They made us dinner a little later than usual and were super nice about it. But if you do get there late, you will have to take a taxi from the train station because the bus stops running in late afternoon. (The taxi ride was about 10-15 minutes, and something like 2000-3000 yen, if I remember correctly.) And if you are late enough to have missed the last bus, depending on the time of year, it may be dark when you walk on the forest path -- so bring a flashlight, or have a flashlight app on your phone, just in case!
The only issue for us was that the water was so hot in a couple of the baths that we couldn't get in (but if you expect this, you can start adding cold water from the tap immediately and just come back a little later for your bath). Also, there is no shower. The hot spring water has a ton of minerals in it, which makes your skin feel great but would inevitably clog a shower, so the only way to do the soap portion of your bathing is the old school way, by scooping up bowlfuls of water from the bath to pour over yourself. This is a very authentic experience, but fussy travelers may not like it compared to more modern onsen or sento facilities that also have a shower. The hotel has not been updated in a long time, adding to its mountain-lodge feel. We liked it just fine, but here again a more picky person may see it as "old" instead of "charming." Another reviewer said their room smelled like cigarette smoke, which worried me, but I did not smell anything. So this may not be a good match for more picky travelers, or for travelers with limited mobility (since you have to walk a good distance on a forest path with your luggage). But for adventurous travelers looking for a rustic onsen experience, do not be afraid: it was clean and friendly and authentic.