OkutsuSo Ryokan (奥津荘) is renowned for having among the very best natural hot springs in all of Japan. They get it straight from the source, and it’s nearby. As we were the only guests staying at OkutsuSo this day, we were able to sample all four of the baths (not counting the open-air Onsen bath in our room.) They are:
Kagiyu (鍵湯) – Indoor, gender-segregated Onsen bath (it switches between male-only and female-only on alternating days.) Named after the fact that the Lord during the feudal era loved this bath so much that he ordered the room to the bath to be locked, and only accessible by him.
Tachiyu ( 立湯) – Indoor, gender-segregated Onsen bath (it switches between male-only and female-only on alternating days.) “Tachi” or “Tatsu” means “to stand” – it’s so named because of the bath being relatively deep. Up to 130 centimeters at its deepest point.
Izumi-no-yu (泉の湯) – Indoor, private rental Onsen bath (貸切風呂.) This is for private use – free of charge – to any guests staying at OkutsuSo. If it’s not occupied, you’re free to use it.
Kawa-no-yu (川の湯) – Semi-open-air private rental Onsen bath (貸切露天風呂.) This is for private use – free of charge – to any guests staying at OkutsuSo. If it’s not occupied, you’re free to use it. “Kawa” means “River” in Japanese, and it’s so named because you can get a view of the river (slightly obscured for privacy reasons) while taking in fresh air during the bathing session.
AloJapan.com