Mixing hot spring water into a cold plunge bath. From the moment I heard that idea, I couldn't think about anything else. Natural groundwater drawn from deep underground, blended with hot spring source water. No chiller. No circulation. A free-flowing bath kept at 14–16°C. Just those conditions alone were enough for me to imagine how incredibly good it would feel. Through all my travels, I've experienced firsthand just how wonderful a naturally flowing cold plunge with no chiller can be. And now that softness would be enriched with the silky texture of hot spring water. What on earth would it feel like? The thought alone made me tremble. That morning, I'd been moved by the extraordinary sauna and architecture at Fujiyama Onsen, and after getting out of the bath, I'd caught my first full view of Mount Fuji. From there I'd cycled around Lake Kawaguchi and soaked in breathtaking views of the mountain until the sun went down. I returned the rental bike and boarded the Fujikyu Railway. The evening sauna journey was about to begin. Tsuru City Station was unmanned. When I stepped through the ticket gate, it was dark and there wasn't a soul in sight. The emptiness was so complete, I almost doubted whether a renowned onsen facility in Yamanashi could really be nearby. But after walking a few minutes, the building I'd seen in photos came into view. The parking lot was full of cars. I took a photo of the exterior and stepped inside. The quiet outside the station felt like a lie — inside, the place was buzzing with life. Families, groups of friends, solo visitors. All kinds of people moved through the space, and the energy was infectious. I think facilities generally fall into two types. One is the kind designed for quiet, solitary self-care. The other is more like a community hub — lively with families and friends, yet welcoming enough for solo guests too. Yamanashi Tomareru Onsen Yorimichi no Yu was clearly the latter. And that liveliness felt just right. I checked in at the front desk and made my way to the main bath area. The indoor baths were, honestly, nothing special — they felt like a standard super sento. But then my eyes landed on the free-flowing cold plunge. Water was pouring into it steadily and generously. It was positioned right at the exit of the sauna room, so you could step out and slip in without a moment's detour. Wasn't that perfect? When I moved to the outdoor area, the whole atmosphere transformed. A large, free-flowing open-air rock bath stood there with a commanding presence. I'd save that for later. I rinsed off and warmed up in the indoor carbonated bath, then headed to the sauna room. First set. The moment I sat down on the top bench, an automatic löyly cycle kicked in. Good timing. A rush of water crashed over the sauna stones, and a few seconds later, a fierce wave of heat swept through the room. The stove was an isness model by Metos — a design that fuses gas far-infrared heating with sauna stones, built to warm you from the core. Whether it was that design or not, the entire room was saturated with heat and humidity. The automatic löyly was so intense I instinctively dropped down a bench. At exactly the same moment, the man sitting next to me did the same. Our eyes met. "That's absolutely brutal, isn't it... ha." The words just slipped out. He laughed too. These small, spontaneous exchanges — that's part of what makes sauna so good. I took in the waves of heat and let my body warm through slowly. A perfect sauna to close out a spectacular day. Let's go all the way. Finally, the moment I'd been waiting for — time for the cold plunge. I rinsed off the sweat and slowly lowered myself into the water. The temperature felt like 14°C. Cold. But within that coldness, something else was present. On top of the soft quality of the groundwater, there was a slippery, silky texture — like the feel of hot spring water. The natural water at Hotel Mount Fuji the night before and at Fujiyama Onsen that morning had both had a crisp, refreshing sharpness. But this cold plunge was different. Gentle, smooth — and though it might sound strange to say this — despite being a cold plunge, there was a warmth to it. It was so comfortable I nearly forgot I was in a cold bath at all. I moved to the outdoor area and let my whole body sink into a chair, gazing up at the night sky. The night breeze of Yamanashi drifted quietly over my body, still cooled by the plunge. I could feel the fine hairs on my skin standing up. To think that at the end of such a day, an experience like this was waiting. Second set. With the afterglow of the outdoor rest still in my body, I first soaked in the outdoor natural hot spring. The water poured vigorously into the free-flowing rock bath. Sinking into natural hot spring water after a sublime cold plunge and outdoor rest — this routine is a staple at any facility with excellent onsen water. I noticed something here: the design of this rock bath was remarkably well thought out. The backrest was angled, allowing you to relax in a natural, reclining posture. Many facilities have a straight 90-degree back, which puts strain on the neck when you try to lean back and is hard to maintain for long. On top of that, there were spots around the rock bath where you could rest your head — you could actually lie back and soak. It felt like the designers had visualized how a person actually moves when bathing. A subtle consideration, but one that makes a significant difference to the quality of the experience. After warming myself back up thoroughly, I returned to the sauna. Wrapped again in the heat of the isness stove, I plunged into the cold bath. Even the second time, the sense of wonder didn't fade. The distinctive, gentle softness of groundwater blended with hot spring water enveloped me once more. I collapsed into the outdoor chair and stayed there, vacant and motionless for a while. Third set. I decided to join the aufguss event. A staff member entered the sauna room. It was a quiet aufguss. After pouring aromatic water over the sauna stones, they fanned in silence, methodically and without fuss. No theatrical performance — just steady, focused work. Each person received three rounds of heat waves. This sauna room was already scorching from the automatic löyly alone; with aufguss on top of that, it was even more intense. That intensity was exactly right for the end of a day like this. I left early. When I join aufguss events, I generally slip out before the end. The reason is simple: if you stay until the finish, the cold plunge becomes packed. To have a truly good experience, you need to move differently from the crowd. Leave early and you can enjoy the cold plunge to your heart's content. I do feel a little bad toward the staff, but I always make sure to say thank you as I go. That way, I don't feel any guilt. I finished with one last round in that sublime cold plunge, and my sauna session for the day was complete.

Mixing hot spring water into a cold plunge bath. From the moment I heard that idea, I couldn't think about anything else. Natural groundwater drawn from deep underground, blended with hot spring source water. No chiller. No circulation. A free-flowing bath kept at 14–16°C. Just those conditions alone were enough for me to imagine how incredibly good it would feel. Through all my travels, I've experienced firsthand just how wonderful a naturally flowing cold plunge with no chiller can be. And now that softness would be enriched with the silky texture of hot spring water. What on earth would it feel like? The thought alone made me tremble. That morning, I'd been moved by the extraordinary sauna and architecture at Fujiyama Onsen, and after getting out of the bath, I'd caught my first full view of Mount Fuji. From there I'd cycled around Lake Kawaguchi and soaked in breathtaking views of the mountain until the sun went down. I returned the rental bike and boarded the Fujikyu Railway. The evening sauna journey was about to begin. Tsuru City Station was unmanned. When I stepped through the ticket gate, it was dark and there wasn't a soul in sight. The emptiness was so complete, I almost doubted whether a renowned onsen facility in Yamanashi could really be nearby. But after walking a few minutes, the building I'd seen in photos came into view. The parking lot was full of cars. I took a photo of the exterior and stepped inside. The quiet outside the station felt like a lie — inside, the place was buzzing with life. Families, groups of friends, solo visitors. All kinds of people moved through the space, and the energy was infectious. I think facilities generally fall into two types. One is the kind designed for quiet, solitary self-care. The other is more like a community hub — lively with families and friends, yet welcoming enough for solo guests too. Yamanashi Tomareru Onsen Yorimichi no Yu was clearly the latter. And that liveliness felt just right. I checked in at the front desk and made my way to the main bath area. The indoor baths were, honestly, nothing special — they felt like a standard super sento. But then my eyes landed on the free-flowing cold plunge. Water was pouring into it steadily and generously. It was positioned right at the exit of the sauna room, so you could step out and slip in without a moment's detour. Wasn't that perfect? When I moved to the outdoor area, the whole atmosphere transformed. A large, free-flowing open-air rock bath stood there with a commanding presence. I'd save that for later. I rinsed off and warmed up in the indoor carbonated bath, then headed to the sauna room. First set. The moment I sat down on the top bench, an automatic löyly cycle kicked in. Good timing. A rush of water crashed over the sauna stones, and a few seconds later, a fierce wave of heat swept through the room. The stove was an isness model by Metos — a design that fuses gas far-infrared heating with sauna stones, built to warm you from the core. Whether it was that design or not, the entire room was saturated with heat and humidity. The automatic löyly was so intense I instinctively dropped down a bench. At exactly the same moment, the man sitting next to me did the same. Our eyes met. "That's absolutely brutal, isn't it... ha." The words just slipped out. He laughed too. These small, spontaneous exchanges — that's part of what makes sauna so good. I took in the waves of heat and let my body warm through slowly. A perfect sauna to close out a spectacular day. Let's go all the way. Finally, the moment I'd been waiting for — time for the cold plunge. I rinsed off the sweat and slowly lowered myself into the water. The temperature felt like 14°C. Cold. But within that coldness, something else was present. On top of the soft quality of the groundwater, there was a slippery, silky texture — like the feel of hot spring water. The natural water at Hotel Mount Fuji the night before and at Fujiyama Onsen that morning had both had a crisp, refreshing sharpness. But this cold plunge was different. Gentle, smooth — and though it might sound strange to say this — despite being a cold plunge, there was a warmth to it. It was so comfortable I nearly forgot I was in a cold bath at all. I moved to the outdoor area and let my whole body sink into a chair, gazing up at the night sky. The night breeze of Yamanashi drifted quietly over my body, still cooled by the plunge. I could feel the fine hairs on my skin standing up. To think that at the end of such a day, an experience like this was waiting. Second set. With the afterglow of the outdoor rest still in my body, I first soaked in the outdoor natural hot spring. The water poured vigorously into the free-flowing rock bath. Sinking into natural hot spring water after a sublime cold plunge and outdoor rest — this routine is a staple at any facility with excellent onsen water. I noticed something here: the design of this rock bath was remarkably well thought out. The backrest was angled, allowing you to relax in a natural, reclining posture. Many facilities have a straight 90-degree back, which puts strain on the neck when you try to lean back and is hard to maintain for long. On top of that, there were spots around the rock bath where you could rest your head — you could actually lie back and soak. It felt like the designers had visualized how a person actually moves when bathing. A subtle consideration, but one that makes a significant difference to the quality of the experience. After warming myself back up thoroughly, I returned to the sauna. Wrapped again in the heat of the isness stove, I plunged into the cold bath. Even the second time, the sense of wonder didn't fade. The distinctive, gentle softness of groundwater blended with hot spring water enveloped me once more. I collapsed into the outdoor chair and stayed there, vacant and motionless for a while. Third set. I decided to join the aufguss event. A staff member entered the sauna room. It was a quiet aufguss. After pouring aromatic water over the sauna stones, they fanned in silence, methodically and without fuss. No theatrical performance — just steady, focused work. Each person received three rounds of heat waves. This sauna room was already scorching from the automatic löyly alone; with aufguss on top of that, it was even more intense. That intensity was exactly right for the end of a day like this. I left early. When I join aufguss events, I generally slip out before the end. The reason is simple: if you stay until the finish, the cold plunge becomes packed. To have a truly good experience, you need to move differently from the crowd. Leave early and you can enjoy the cold plunge to your heart's content. I do feel a little bad toward the staff, but I always make sure to say thank you as I go. That way, I don't feel any guilt. I finished with one last round in that sublime cold plunge, and my sauna session for the day was complete.