You may bathe in the sacred onsen water of Mt. Yudono at the Sanrojo Mountain Lodge that is located right next to the massive tori gate. These baths are open both to guests staying at the lodge and to the general public. This hotspring water is rich in the minerals of the mountains and the same water that is found at the shrine area of this mountain.
Please note that these are public baths and that there are no private bathing option here. See below for the two bath types of this lodge.