We shall visit Hirugami Onsen in September this year. I have learnt from the official website of Hirugami Onsen that there’s a bus running between Kamisuwa and Hirugami Onsen.
Can we just take a single ride from Hirugami Onsen to Kamisuwa?
Where can we make reservation?
The Hirugami-Kamisuwa Bus is set up for round-trip travel only; however, you can take a one-way trip as long as you’re willing to still pay the round-trip price (2,500 yen).
To make a reservation, email your hotel in Hirugami Onsen. They will arrange it for you. (Reservations must be made by 17:30 at least three days in advance of use.)
I hope that helps answer your question!