Whether it was the effect of yesterday's Shirahama Onsen, I woke up feeling absolutely amazing. The afterglow of sinking into the famous Shirahama waters at Hotel Kawakyu's Royal Spa, then doing 3 sets while gazing out at the evening sea, still lingered in my body. I took a morning walk, had breakfast, and drank a coffee in my room before getting ready to head out. Today's destination: Aridagawa Onsen Hikari no Yu. This place had been on my radar for a while. There are good reasons why I considered it unmissable for anyone wanting to enjoy hot springs, sauna, and a cold plunge in Wakayama. A hot-cold alternating bath using 41°C natural hot spring water and a 28°C cold mineral spring, the world's first onsen steam sauna that vaporizes the natural source water, a high-temperature sauna with about 150kg of Kishu Binchotan charcoal lining every wall, and a cold plunge bath fed by the natural subterranean water of the Arida River. That description alone should be enough to make any hot spring or sauna enthusiast want to experience it immediately. I arrived at the facility at 8 a.m., checked in at the front desk, and made my way to the main bath. The exterior and interior are those of a typical super sento. But I knew better. The equipment lined up here was anything but ordinary. Stepping into the main bath, I spotted the high-temperature Binchotan charcoal sauna immediately to the right, and just in front of it, a 41°C hot spring and a 28°C cold mineral spring sitting side by side. Beyond a corridor lay the outdoor bath area, where you could enjoy the hot springs while gazing at trees and sky. The relaxation space was well-equipped too — not just chairs, but a tatami area where you could lie flat. With spring just around the corner, outdoor air bathing was going to be at its very best. Before getting into the sauna, I decided to start with the hot-cold alternating bath. Having the 41°C hot spring and the 28°C cold mineral spring right next to each other was basically an open invitation. I sank into the 41°C hot spring and let my body warm up. The water is a sodium chloride spring with a wonderfully smooth texture. Within just a few minutes, I was glowing with warmth. The power of natural hot springs is remarkable. Then I stepped over the edge into the 28°C cold mineral spring and submerged myself completely. It felt incredible — not too hot, not too cold. I could almost imagine reaching a state of totonou from this alone, without ever touching a sauna. After cooling down in the cold spring, I stepped back over into the 41°C hot spring. In that instant, a shiver of pleasure ran through my entire body. The sensation of warm water rushing over a body that had just been cooled is a completely different kind of pleasure from stepping into a cold plunge after a sauna. I moved back to the cold spring, then returned again. I repeated this about 5 times. This was the most pleasurable hot-cold alternating bath of my life. The temperature calibration is perfect. 41°C and 28°C. That difference in temperature produces a supreme state of relaxation. I was already completely satisfied — and I hadn't even been in the sauna yet. It had been so good I'd almost forgotten. First set. I entered the high-temperature sauna lined wall-to-wall with Kishu Binchotan charcoal. About 150kg of Binchotan, made from the native ubame oak of Kishu, was arranged across every wall surface. A showerhead was mounted above a stove piled high with stones, delivering an automatic löyly system. The room temperature was around 90°C, and perhaps due to the far-infrared rays emitted by the Binchotan, I felt a warmth spreading from deep inside my body. The charcoal covering the walls in particular sent gentle heat radiating in from my back. In most saunas, only the surface of the skin heats up without the warmth truly penetrating deep — but here, without any sense of breathlessness, I naturally warmed from the inside out. So this is what Binchotan charcoal can do. I submerged myself in the Arida River subterranean water cold plunge bath. The temperature was around 18°C, with pure natural spring water flowing through continuously. It is reportedly clean enough to drink. The soft, enveloping quality of the water was deeply pleasant. Because it is natural spring water, the temperature does fluctuate with the seasons — it might feel lukewarm in summer, and likely gets quite cold in winter. There is no doubt that this current season is the most comfortable. What good timing to have come now. I stepped out to the outdoor space and lay down on the tatami. I breathed in the fresh Arida River air as deeply as I could. I briefly lost consciousness. For the second set, I started with the steam sauna — labeled the world's first onsen steam sauna. Using a fine-particle steam called heated water vapor, produced by vaporizing the natural source water at ultra-high temperature, it allows you to absorb the benefits of the hot spring both through your skin and through your breathing. The temperature was a gentle 50°C, wonderfully comfortable. After warming up slowly while wrapped in steam, I moved directly into the high-temperature Binchotan charcoal sauna. Having warmed up with the steam sauna, sweat poured off me like a waterfall the moment I stepped in. This sauna really does something remarkable to the body. The heat stored from the inside by the far-infrared rays, then released all at once in the high-temperature sauna — I was moved. I submerged again in the Arida River spring water cold plunge, then lay outside to rest. I repeated this one more time, finishing after 3 sets in total.

Whether it was the effect of yesterday's Shirahama Onsen, I woke up feeling absolutely amazing. The afterglow of sinking into the famous Shirahama waters at Hotel Kawakyu's Royal Spa, then doing 3 sets while gazing out at the evening sea, still lingered in my body. I took a morning walk, had breakfast, and drank a coffee in my room before getting ready to head out. Today's destination: Aridagawa Onsen Hikari no Yu. This place had been on my radar for a while. There are good reasons why I considered it unmissable for anyone wanting to enjoy hot springs, sauna, and a cold plunge in Wakayama. A hot-cold alternating bath using 41°C natural hot spring water and a 28°C cold mineral spring, the world's first onsen steam sauna that vaporizes the natural source water, a high-temperature sauna with about 150kg of Kishu Binchotan charcoal lining every wall, and a cold plunge bath fed by the natural subterranean water of the Arida River. That description alone should be enough to make any hot spring or sauna enthusiast want to experience it immediately. I arrived at the facility at 8 a.m., checked in at the front desk, and made my way to the main bath. The exterior and interior are those of a typical super sento. But I knew better. The equipment lined up here was anything but ordinary. Stepping into the main bath, I spotted the high-temperature Binchotan charcoal sauna immediately to the right, and just in front of it, a 41°C hot spring and a 28°C cold mineral spring sitting side by side. Beyond a corridor lay the outdoor bath area, where you could enjoy the hot springs while gazing at trees and sky. The relaxation space was well-equipped too — not just chairs, but a tatami area where you could lie flat. With spring just around the corner, outdoor air bathing was going to be at its very best. Before getting into the sauna, I decided to start with the hot-cold alternating bath. Having the 41°C hot spring and the 28°C cold mineral spring right next to each other was basically an open invitation. I sank into the 41°C hot spring and let my body warm up. The water is a sodium chloride spring with a wonderfully smooth texture. Within just a few minutes, I was glowing with warmth. The power of natural hot springs is remarkable. Then I stepped over the edge into the 28°C cold mineral spring and submerged myself completely. It felt incredible — not too hot, not too cold. I could almost imagine reaching a state of totonou from this alone, without ever touching a sauna. After cooling down in the cold spring, I stepped back over into the 41°C hot spring. In that instant, a shiver of pleasure ran through my entire body. The sensation of warm water rushing over a body that had just been cooled is a completely different kind of pleasure from stepping into a cold plunge after a sauna. I moved back to the cold spring, then returned again. I repeated this about 5 times. This was the most pleasurable hot-cold alternating bath of my life. The temperature calibration is perfect. 41°C and 28°C. That difference in temperature produces a supreme state of relaxation. I was already completely satisfied — and I hadn't even been in the sauna yet. It had been so good I'd almost forgotten. First set. I entered the high-temperature sauna lined wall-to-wall with Kishu Binchotan charcoal. About 150kg of Binchotan, made from the native ubame oak of Kishu, was arranged across every wall surface. A showerhead was mounted above a stove piled high with stones, delivering an automatic löyly system. The room temperature was around 90°C, and perhaps due to the far-infrared rays emitted by the Binchotan, I felt a warmth spreading from deep inside my body. The charcoal covering the walls in particular sent gentle heat radiating in from my back. In most saunas, only the surface of the skin heats up without the warmth truly penetrating deep — but here, without any sense of breathlessness, I naturally warmed from the inside out. So this is what Binchotan charcoal can do. I submerged myself in the Arida River subterranean water cold plunge bath. The temperature was around 18°C, with pure natural spring water flowing through continuously. It is reportedly clean enough to drink. The soft, enveloping quality of the water was deeply pleasant. Because it is natural spring water, the temperature does fluctuate with the seasons — it might feel lukewarm in summer, and likely gets quite cold in winter. There is no doubt that this current season is the most comfortable. What good timing to have come now. I stepped out to the outdoor space and lay down on the tatami. I breathed in the fresh Arida River air as deeply as I could. I briefly lost consciousness. For the second set, I started with the steam sauna — labeled the world's first onsen steam sauna. Using a fine-particle steam called heated water vapor, produced by vaporizing the natural source water at ultra-high temperature, it allows you to absorb the benefits of the hot spring both through your skin and through your breathing. The temperature was a gentle 50°C, wonderfully comfortable. After warming up slowly while wrapped in steam, I moved directly into the high-temperature Binchotan charcoal sauna. Having warmed up with the steam sauna, sweat poured off me like a waterfall the moment I stepped in. This sauna really does something remarkable to the body. The heat stored from the inside by the far-infrared rays, then released all at once in the high-temperature sauna — I was moved. I submerged again in the Arida River spring water cold plunge, then lay outside to rest. I repeated this one more time, finishing after 3 sets in total.