Make the most of your foray into the mountains: this inn, only open 123 days each year, is like staying at a mountain hut without having to walk five hours to get there. There are simple tatami rooms with shared facilities, but the food is good, the onsen is hot and the air is fresh. No English is spoken, so come prepared.
Note that early check-in is required (between 10.30am and 3pm) to ensure guests are not navigating the treacherous mountain road in the dark. Also, due to the remoteness, there is no telephone or mobile service, or wi-fi.
The lodge also operates a shokudō (casual eatery) between 11.30am and 1pm, with simple meals such as ramen and curry rice.
There are two shuttle buses per day from Sōunkyō Onsen for overnight guests (reservations necessary), but having your own wheels is the best option. If you're not staying, you can use the onsen for ¥700.