We have no photographs of the onsen.
The Ryokan (traditional Japanese inn) was built where it was, and has existed in one form or another for 850 years because of the hot spring in a cave under the Ryokan.
And that hot spring is the onsen.
There were two ways to sit in the hot water.
One half was styled as a roman bath, and had clearly been there for many years, made obvious by the handmade nature of the tiles, the design aesthetic of the room, and the impressive mineral accretions on parts of the structure. A definite time capsule or a more romantic age.
The other half was the cave. There had clearly been carving out – to make a bigger area, to make a more regular shaped pool, and some seats had been created and tiled. But all we had to do was paddle back a bit, and there was uncarved rock, and niches where lamps/lanterns had been placed in the days before electrical lighting had made it down into the cave.
The air was lovely and steamy, the water milky and soft. It was a wonderful place to soak, warm up, and float peacefully, and truly appreciate the absolutely unique experience it was.
And while we were recovering from the hot spring adventure, they brought in dinner.
And that requires a whole entry of its own.