The name tells you who this place belongs to. Ryujin means Dragon God, and according to legend, the Buddhist monk Kukai -- known posthumously as Kobo Daishi -- discovered these waters after a dream visitation from Nanda, the Dragon King of the Sea. That was in the ninth century. But the hot springs had already been steaming for at least two hundred years before Kukai arrived. In the seventh century, En no Gyoja, the wandering ascetic who founded the mountain religion of Shugendo, found these mineral-rich waters bubbling up in a remote gorge of the Hidaka River valley. Thirteen centuries later, the water still rises, still clear, still silky with dissolved sodium bicarbonate, in a narrow valley so deep in the Kii Mountains that even the Tokugawa shoguns considered it a proper retreat from the world.
Ryujin Onsen holds one of Japan's most coveted designations: it is one of the three Bijin-no-yu, or Beautiful Women Hot Springs, alongside Kawanaka Onsen in Gunma Prefecture and Yunokawa Onsen in Shimane Prefecture. The distinction is not mere marketing. The water's high sodium bicarbonate concentration gives it a slippery, almost soapy texture that dissolves dead skin cells and leaves a smooth finish. In traditional Japanese bathing culture, this effect was considered a mark of divine favor -- proof that the Dragon God blessed the waters. The hot springs use a kakenagashi system, meaning water flows directly from the source to the bath without recirculation, preserving every mineral trace exactly as it emerges from the earth. Bathers describe the sensation as stepping into warm silk.
During the Edo period, from 1603 to 1868, the Tokugawa ruling family of the Kii domain claimed Ryujin Onsen as their private retreat. Their castle sat in Wakayama City, hours away along mountain roads, but the difficulty of the journey was precisely the point -- Ryujin offered isolation that even a shogun could not find at home. The family built lodgings befitting their status, and two of those names survive today as ryokan inns: Kamigoten, meaning Royal Palace, and Shimogoten, meaning Lower Palace. The distinction between the two reflected the rigid hierarchy of Edo-era Japan, where even a hot spring resort observed feudal rank. Guests at Shimogoten today sleep in rooms that echo three centuries of hospitality, the wooden architecture creaking softly above the sound of the Hidaka River below.
Ryujin Onsen sits within the Koya-Ryujin Quasi-National Park, a protected landscape of beech forests and mountain ridges running at elevations around 1,000 meters. The Koya-Ryujin Skyline road connects the hot spring village to Mount Koya, the sacred headquarters of Shingon Buddhism founded by the same Kobo Daishi who is credited with establishing the onsen. This is not coincidence. The route between Koya and Ryujin has been a pilgrims' path for centuries, threading through forests where the autumn foliage ignites in reds and golds each October. The hot spring inns line the uppermost reach of the Hidaka River valley, their wooden facades pressed against steep hillsides, smoke from bathhouse vents drifting through cedar groves. It is a landscape that looks much as it did when the first monks arrived, seeking purification in waters they believed a dragon had blessed.
Unlike many of Japan's famous onsen towns, Ryujin has never developed into a large resort. The village remains small, its handful of ryokan and bathhouses strung along the river in a settlement that feels closer to a mountain hamlet than a tourist destination. The public bathhouse Motoyu -- meaning original source -- marks the spot where the springs were first discovered and remains the heart of the community. Visitors come for the water itself, not for neon signs or amusement. The remoteness that attracted shoguns and monks continues to define the experience: reaching Ryujin requires a winding drive through the Kii Mountains or a bus ride from Tanabe City that itself becomes part of the journey. In a country where modernity has reshaped most landscapes, this corner of Wakayama Prefecture preserves something older -- the simple act of lowering yourself into mineral water that has been flowing since before Japan had a written history.
Located at 33.96°N, 135.56°E in the mountainous interior of the Kii Peninsula, Wakayama Prefecture. The onsen village sits in a narrow gorge along the upper Hidaka River at approximately 300-400 meters elevation, surrounded by peaks exceeding 1,000 meters within the Koya-Ryujin Quasi-National Park. From the air, look for the thin ribbon of the Hidaka River valley cutting through dense forested mountains. The Koya-Ryujin Skyline road is visible as a ridgeline route connecting northwest toward Mount Koya. Nearest airport is Nanki-Shirahama Airport (RJBD), approximately 30 nautical miles to the south. Best viewed at 3,000-5,000 feet AGL to appreciate the contrast between the narrow valley settlement and the surrounding mountain wilderness.