This was finally my last facility. If I could, I'd stay for months and visit every single hot spring and sauna in the Kanto region. But that's not realistic — I have to go home. That's exactly why I do thorough research beforehand, so I can make the most of my limited time. During that research, I found a place that uses naturally flowing hot spring water in every single bath — including the cold plunge — and has two saunas to boot. Digging deeper, it seemed to rank among the very best in Kanagawa Prefecture. That facility is Asahiyu Gensen Yuiru. I took a taxi from Keikyu Kawasaki Station and arrived at my destination in about ten minutes. It sits quietly along the roadside, the kind of place you'd walk right past if you weren't paying attention. I'd assumed it was a regular super sento, but a two-hour entry came to 2,480 yen — a fairly steep price. I was hoping the hot springs, sauna, and cold plunge would be worth every yen. Once I changed and stepped into the main bath area, I was struck by how compact it was. It felt even smaller than the photos suggested — more like a neighborhood sento in scale. And yet, the natural hot spring water flowing into those baths was the real deal, the kind you rarely get to experience. This spring was struck at a depth of 1,200 meters underground, and it contains roughly 25 times the mineral concentration required to qualify as a medicinal spring — which it officially is. Japan has a tradition called toji, the practice of healing illness by soaking in hot springs. But not just any hot spring will do. Only springs with an overwhelming concentration of minerals at the level of a certified medicinal spring can truly deliver those effects. When I actually sank into the water, it felt like melting — like being submerged in a bath of lotion. The spring water wrapped around my body and gave me a sense of bliss I can only describe as extraordinary. This spring is also known as the "hot spring of heat," and sure enough, my entire body was warming from the inside after just a few minutes. Based on my research, this same spring water is used in the cold plunge too, and I could already feel the dopamine building at the thought of what that might feel like. I've enjoyed many natural hot springs over the years, but the spring at Asahiyu Gensen Yuiru is in a class of its own. After warming up in the hot spring, it was time for the sauna. Asahiyu Gensen Yuiru has two saunas: 1. Löyly Sauna: A sauna room with temperatures exceeding 100°C. Regular automatic löyly pours a substantial amount of water over the sauna stones, filling the entire room with an intense wave of heat. 2. Aufguss Sauna: A spacious sauna room set at 85°C, dedicated to aufguss sessions held every hour. When it's not busy, you can lie down and enjoy a leisurely sauna session. I started with a visit to the Löyly Sauna, just to say hello. With temperatures over 100°C, it was intensely hot — but the steam from the löyly kept the humidity high, so there was none of that sharp, prickling sensation on the skin. It was clearly designed for comfortable sauna bathing. No television, just a quiet space where you could sink into meditation. After warming up for a while, I felt my limits approaching and headed to the cold plunge. The cold plunge was fed by that very same extraordinary hot spring water. After rinsing off my sweat, I was once again enveloped in that silky, melting sensation. In terms of sheer smoothness, this might have been the finest water I've ever encountered in my life. It was that soft. And the temperature was 13°C — genuinely cold. But that overwhelming silkiness meant it never felt harsh or biting on the skin; it simply felt wonderful. The best cold plunge I've ever had. Afterward, I rested in the dedicated relaxation area and found myself unable to think about anything at all. If you want to experience the ultimate cold plunge, this is a facility you absolutely must visit. For my second set, I savored the Aufguss Sauna. The timing worked out perfectly — an aufguss event was just about to begin, so I joined in. The heater (neppashi) performed towel-waving choreography to music. For over ten minutes, they kept swinging the towel in rhythm with the music, and by the second half, you could see their shoulders starting to give out. Cheers of encouragement naturally rose from the guests. By the end of the event, the room was full of applause and praise. I, for my part, murmured my thanks in a voice barely louder than a mosquito's buzz. After the aufguss, I dove back into that glorious cold plunge. What makes the cold plunge at Asahiyu Gensen Yuiru so special isn't just that it uses hot spring water. Apparently, when they designed it, they deliberately made it deep enough to fully submerge yourself. That means you can immerse yourself head to toe in this extraordinary mineral spring water. There's nothing quite like a cold plunge that's both deep and wide. Add to that the fact that it's filled with top-tier hot spring water, and it's no wonder this place has become one of Kanagawa's most popular facilities. While resting in the relaxation area, I apparently lost consciousness entirely. I don't know how many minutes I was out, but when I came back to my senses, I decided to go for a third set. For the third set, I returned to the Löyly Sauna. I wanted to experience what truly scorching löyly felt like. Deliberately taking a seat on the top bench, I waited for the löyly to begin. Then the lighting in the room changed, and it started. An absurd amount of water was poured over the sauna stones — it looked like someone had just thrown an entire bucket directly onto them. In an instant, a ferocious wave of heat surged through the room. It was so intense I half-thought my face and ears were on fire — I could actually feel something close to pain. Breathing became difficult, and I started to panic. I scrambled down from the top bench to the lower level to escape the crisis. But even on the lower bench, the heat was still overwhelming. I had never experienced löyly this brutal. Out of curiosity, I glanced back up at the top bench where I'd been sitting, and there was the person who had been beside me the whole time — arms folded, eyes closed, radiating the aura of a samurai. Not a single twitch through all that heat, still holding that powerful posture while enduring the full force of the steam. What incredible fortitude. I have no idea who they were, but I felt a genuine sense of awe as I slipped out of the sauna ahead of them. I plunged back into the glorious cold plunge one final time, and with that, my sauna session for the day was complete.

This was finally my last facility. If I could, I'd stay for months and visit every single hot spring and sauna in the Kanto region. But that's not realistic — I have to go home. That's exactly why I do thorough research beforehand, so I can make the most of my limited time. During that research, I found a place that uses naturally flowing hot spring water in every single bath — including the cold plunge — and has two saunas to boot. Digging deeper, it seemed to rank among the very best in Kanagawa Prefecture. That facility is Asahiyu Gensen Yuiru. I took a taxi from Keikyu Kawasaki Station and arrived at my destination in about ten minutes. It sits quietly along the roadside, the kind of place you'd walk right past if you weren't paying attention. I'd assumed it was a regular super sento, but a two-hour entry came to 2,480 yen — a fairly steep price. I was hoping the hot springs, sauna, and cold plunge would be worth every yen. Once I changed and stepped into the main bath area, I was struck by how compact it was. It felt even smaller than the photos suggested — more like a neighborhood sento in scale. And yet, the natural hot spring water flowing into those baths was the real deal, the kind you rarely get to experience. This spring was struck at a depth of 1,200 meters underground, and it contains roughly 25 times the mineral concentration required to qualify as a medicinal spring — which it officially is. Japan has a tradition called toji, the practice of healing illness by soaking in hot springs. But not just any hot spring will do. Only springs with an overwhelming concentration of minerals at the level of a certified medicinal spring can truly deliver those effects. When I actually sank into the water, it felt like melting — like being submerged in a bath of lotion. The spring water wrapped around my body and gave me a sense of bliss I can only describe as extraordinary. This spring is also known as the "hot spring of heat," and sure enough, my entire body was warming from the inside after just a few minutes. Based on my research, this same spring water is used in the cold plunge too, and I could already feel the dopamine building at the thought of what that might feel like. I've enjoyed many natural hot springs over the years, but the spring at Asahiyu Gensen Yuiru is in a class of its own. After warming up in the hot spring, it was time for the sauna. Asahiyu Gensen Yuiru has two saunas: 1. Löyly Sauna: A sauna room with temperatures exceeding 100°C. Regular automatic löyly pours a substantial amount of water over the sauna stones, filling the entire room with an intense wave of heat. 2. Aufguss Sauna: A spacious sauna room set at 85°C, dedicated to aufguss sessions held every hour. When it's not busy, you can lie down and enjoy a leisurely sauna session. I started with a visit to the Löyly Sauna, just to say hello. With temperatures over 100°C, it was intensely hot — but the steam from the löyly kept the humidity high, so there was none of that sharp, prickling sensation on the skin. It was clearly designed for comfortable sauna bathing. No television, just a quiet space where you could sink into meditation. After warming up for a while, I felt my limits approaching and headed to the cold plunge. The cold plunge was fed by that very same extraordinary hot spring water. After rinsing off my sweat, I was once again enveloped in that silky, melting sensation. In terms of sheer smoothness, this might have been the finest water I've ever encountered in my life. It was that soft. And the temperature was 13°C — genuinely cold. But that overwhelming silkiness meant it never felt harsh or biting on the skin; it simply felt wonderful. The best cold plunge I've ever had. Afterward, I rested in the dedicated relaxation area and found myself unable to think about anything at all. If you want to experience the ultimate cold plunge, this is a facility you absolutely must visit. For my second set, I savored the Aufguss Sauna. The timing worked out perfectly — an aufguss event was just about to begin, so I joined in. The heater (neppashi) performed towel-waving choreography to music. For over ten minutes, they kept swinging the towel in rhythm with the music, and by the second half, you could see their shoulders starting to give out. Cheers of encouragement naturally rose from the guests. By the end of the event, the room was full of applause and praise. I, for my part, murmured my thanks in a voice barely louder than a mosquito's buzz. After the aufguss, I dove back into that glorious cold plunge. What makes the cold plunge at Asahiyu Gensen Yuiru so special isn't just that it uses hot spring water. Apparently, when they designed it, they deliberately made it deep enough to fully submerge yourself. That means you can immerse yourself head to toe in this extraordinary mineral spring water. There's nothing quite like a cold plunge that's both deep and wide. Add to that the fact that it's filled with top-tier hot spring water, and it's no wonder this place has become one of Kanagawa's most popular facilities. While resting in the relaxation area, I apparently lost consciousness entirely. I don't know how many minutes I was out, but when I came back to my senses, I decided to go for a third set. For the third set, I returned to the Löyly Sauna. I wanted to experience what truly scorching löyly felt like. Deliberately taking a seat on the top bench, I waited for the löyly to begin. Then the lighting in the room changed, and it started. An absurd amount of water was poured over the sauna stones — it looked like someone had just thrown an entire bucket directly onto them. In an instant, a ferocious wave of heat surged through the room. It was so intense I half-thought my face and ears were on fire — I could actually feel something close to pain. Breathing became difficult, and I started to panic. I scrambled down from the top bench to the lower level to escape the crisis. But even on the lower bench, the heat was still overwhelming. I had never experienced löyly this brutal. Out of curiosity, I glanced back up at the top bench where I'd been sitting, and there was the person who had been beside me the whole time — arms folded, eyes closed, radiating the aura of a samurai. Not a single twitch through all that heat, still holding that powerful posture while enduring the full force of the steam. What incredible fortitude. I have no idea who they were, but I felt a genuine sense of awe as I slipped out of the sauna ahead of them. I plunged back into the glorious cold plunge one final time, and with that, my sauna session for the day was complete.