Kanagawa Prefecture is home to Hakone, one of Japan's most famous hot spring destinations. Yet beyond Hakone's well-known resort hotels lie remarkable hidden gems: foot-source springs where thermal water wells up directly through the bath floor, ultra-alkaline waters with pH levels above 10, and centuries-old bathhouses steeped in samurai legend. The Tanzawa mountain range, just an hour from central Tokyo, conceals secluded inns surrounded by pristine forests and crystal-clear streams. Here, we present 8 carefully selected destinations, each offering a distinctive and authentic hot spring experience.
1. Nakagawa Onsen Ao no Sanso (Yamakita Town, Ashigarakami District)
Ao no Sanso is a secluded inn at the deepest reaches of Nakagawa Onsen in the Tanzawa mountains of Kanagawa Prefecture — a spring long known as one of Takeda Shingen's kakushi-yu (hidden healing springs), where the warlord is said to have sent his wounded soldiers to recover after battle. Despite being just 90 minutes from central Tokyo by car, the inn is enveloped in the deep quiet of a mountain valley. It is the sole member inn of the Nihon Hitoyu wo Mamoru Kai (Society for the Preservation of Japan's Hidden Hot Springs) in Kanagawa Prefecture.
The inn's defining feature is its on-site self-flowing spring at an exceptional pH 10.5 — one of the highest alkalinity readings of any hot spring in Japan. The water flows undiluted and chemical-free into all six baths, leaving skin remarkably smooth and soft — a classic "beauty spring." The facility has been recognized as a model site under the Japan Spa Association's natural hot spring certification program.
The grounds span roughly 33,000 m² (one mantubo), attracting over 60 species of wild birds annually. In early summer, the trees fill with the egg masses of Kajika tree frogs, and nightly guided firefly-watching tours are held along the property. Inside the inn, a gallery dedicated to Koji Fukiya — a beloved Taisho and Showa-era lyrical artist who evacuated to nearby Yamakita Town during the war — houses around 2,000 works including original paintings and publications. Nature and art coexist here in a way found nowhere else.
Quality
アルカリ性単純温泉
Temp
40℃ to 42℃
Flow
Natural Source Flow
pH
pH 10.5
0714
AcidicNeutralAlkaline
Use
Stay OK/Day Trip OK
Fee
Adult 1000JPY/Child ---JPY
Hours
| Mon | Tue | Wed | Thu | Fri | Sat | Sun | Hol | |
|---|---|---|---|---|---|---|---|---|
| 10:30 - 14:30 | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ |
Shingen-kan is a long-established inn at the source of Nakagawa Onsen, a spring long known as one of Takeda Shingen's kakure-yu (hidden healing springs), where the famous warlord is said to have sent his wounded soldiers to recover around 450 years ago. Founded in 1910, the inn carries over 115 years of history, and sits deep in the Nishi-Tanzawa valley of Kanagawa Prefecture — just 90 minutes from central Tokyo, yet steeped in mountain stillness and quiet dignity.
The inn's spring, Shingen-ko Kakushi-yu, is an alkaline simple hot spring at an exceptional pH 10.1 — among the highest in Japan. The water leaves skin noticeably silky during bathing and smooth and supple after, earning it the title of "beauty spring." Remarkably, the water can also be drunk, and is said to benefit digestive ailments — making it one of the rare hot springs that nurtures both outer and inner wellbeing.
Quality
アルカリ性単純温泉
Temp
40℃ to 42℃
Flow
Natural Source Flow
pH
pH 10
0714
AcidicNeutralAlkaline
Use
Stay OK/Day Trip OK
Fee
Adult 1000JPY/Child ---JPY
Hours
| Mon | Tue | Wed | Thu | Fri | Sat | Sun | Hol | |
|---|---|---|---|---|---|---|---|---|
| 15:00 - 10:00 | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ |
Kabutoyu Onsen Sanzanro is a solitary inn that has guarded its spring for over 100 years — a source that first welled up when a giant boulder, shaped like a samurai helmet (kabuto), collapsed during the Great Kanto Earthquake of 1923. Nestled deep in the Nanasawa hot spring area of Kanagawa Prefecture, it lives up to its reputation as "the closest hidden hot spring to the Kanto region," offering genuine mountain stillness just an hour from central Tokyo.
The spring flows entirely by natural pressure — no drilling, no mechanical pumping. The cold mineral water (approximately 17.5°C) is heated and served as 100% free-flowing kakenagas hi, with no disinfection or circulation. The moment you dip your hand in, the water's lotion-like, velvety texture is immediately striking. With a pH of 10.1 and 69.7 mg of metasilicic acid, it gently dissolves dead skin cells to leave the complexion soft and smooth — a "beauty spring" held in high regard among discerning hot spring enthusiasts.
The outdoor bath is the inn's crowning glory. The Nanasawa stream flows directly in front of the tub, with dense woodland forming a natural screen around it. In November, the maples blaze red and orange, and soaking beneath the autumn foliage in complete solitude is an experience unique to this inn. The indoor bath, too, has a quiet, contemplative quality. Meals are prepared by the innkeeper himself using carefully selected local ingredients.
Quality
アルカリ性単純温泉
Temp
40℃ to 42℃
Flow
Natural Source Flow
pH
pH 10.1
0714
AcidicNeutralAlkaline
Use
Stay OK/Day Trip OK
Fee
Adult 1400JPY/Child ---JPY
Hours
| Mon | Tue | Wed | Thu | Fri | Sat | Sun | Hol | |
|---|---|---|---|---|---|---|---|---|
| 00:00 - 00:00 | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ |
Book your stay
Iiyama Onsen is a historic spa town nestled along the Koayu River at the eastern edge of the Tanzawa mountain foothills in Atsugi City, Kanagawa Prefecture. Its origins trace back to the late Edo period, and its reputation as a thriving therapeutic bathing destination was significant enough to be documented in the "Kokoku Chishi" (Imperial Geography) published in 1875. Motoyu Ryokan, whose name literally means "original source inn," has faithfully preserved the foundational spring of Iiyama Onsen for generations. The inn's distinctive layout connects its various buildings through narrow alleyways reminiscent of a castle town, transporting guests into a world apart from everyday life. Despite being just 20 minutes from Ebina Service Area and roughly 60 minutes from central Tokyo, the tranquil setting surrounded by Tanzawa's mountains and rivers feels like a secluded retreat deep in the wilderness.\n\nThe crowning jewel of Motoyu Ryokan is its remarkably alkaline hot spring water, boasting a pH of 11.3 — placing it among the highest in all of Japan. This exceptional spring was successfully tapped during development work in 2003, and unlike many alkaline springs that feel viscous or slimy, Iiyama's water is characteristically smooth and silky to the touch. Upon immersion, the alkaline water gently softens the skin's keratin layer, and bathers emerge with a sensation often compared to wearing a layer of luxurious moisturizer. This extraordinary skin-smoothing quality has earned it nationwide acclaim as a "beauty water" spring. The water is classified as a simple alkaline hot spring and is served as free-flowing source water — an increasingly rare luxury in Japan's hot spring world.\n\nThe inn houses several distinct bathing facilities, each offering its own atmosphere. The "Tanuki-buro" (Raccoon Dog Bath) is the main bathhouse that preserves the ambiance of the original Edo-period therapeutic bathing hall, surrounded by charming tanuki figurines that add a playful touch to the historic setting. The "Keiryu Rotenburo" (Mountain Stream Open-Air Bath) provides an immersive experience where bathers can listen to the gentle murmur of the Koayu River while gazing at the ever-changing Tanzawa scenery through the seasons. The "Utaseyu Rotenburo" features a waterfall shower that kneads away tension in tired muscles, while the intimate "Yu-asobi" bath offers a quiet retreat fed by the inn's own private source. A reservable private bath is also available for those seeking a more personal soaking experience.\n\nThe cuisine at Motoyu Ryokan is another compelling reason to visit. The kitchen showcases the bounty of both the Tanzawa mountains and nearby Sagami Bay, crafting seasonal menus that celebrate the region's finest ingredients. Summer brings fresh sweetfish (ayu) from the Koayu River, while winter features the hearty botan-nabe — a rich wild boar hot pot that is a beloved Tanzawa specialty. Atsugi's signature marinated grilled pork (ton-tsuke-yaki) and the inn's original sun-dried sweetfish are standout delicacies not to be missed. The day-trip plan "Yuagari Bijin" (Post-Bath Beauty) starts from 7,500 yen with a meal included, making it easy to enjoy both the springs and the cuisine without an overnight stay. While the inn rewards visitors in every season, the mountain stream open-air bath is particularly spectacular during fresh green season in spring and the fiery foliage of autumn, offering a restorative escape that feels worlds away from the city.
Quality
アルカリ性単純温泉
Temp
40℃ to 42℃
Flow
Natural Source Flow
pH
pH 11.3
0714
AcidicNeutralAlkaline
Use
Stay OK/Day Trip OK
Fee
Adult 7500JPY/Child ---JPY
Hours
| Mon | Tue | Wed | Thu | Fri | Sat | Sun | Hol | |
|---|---|---|---|---|---|---|---|---|
| 11:00 - 15:00 | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ |
Book your stay
Ubako Onsen Shumei-kan is a traditional toji (therapeutic bathing) inn tucked into the forest of Hakone's Ubako area at 885 meters elevation, founded in 1902. Its history stretches back to ancient legend: it is said that Kintoki's mother, the mountain witch Yamauba, washed her son's injured eyes in this spring at the divine instruction of Hakone Gongen — and they healed instantly. This legend earned Ubako Onsen a place among the "Three Great Eye-Healing Hot Springs of Japan."
The inn's greatest treasure is its ashimoto yushutsu-sen — a spring that wells up directly from cracks in the bedrock of the bath floor, marked with a sacred shimenawa rope. The water is completely natural, with no dilution, heating, or disinfection of any kind. During the rainy season in summer, the flow can reach an astonishing 3,000 liters per minute. The spring is a simple hot spring (pH 3.3, mildly acidic), and the clear, soft water leaves a refreshingly clean feeling on the skin characteristic of acidic springs.
The inn occupies a beautifully preserved Taisho-era wooden building on a roughly 10,000 m² plot. It runs no advertising, serves no meals, and admits only around 15 guests per day. The experience is simple and intentional: rent a private room, alternate between soaking and resting, and do nothing else. Private room use is ¥2,500 for 2 hours or ¥4,000 for 4 hours; bathing only (from 15:00) is ¥1,500. Lowering yourself into the spring-fed water in the dimly lit bath, feeling the warmth rise from the ancient bedrock below, is a primal, quietly moving experience unlike anything else in Hakone — and among hot spring enthusiasts, Shumei-kan is simply known as "the most authentic hot spring in Hakone."
Quality
単純温泉
Temp
42℃ to 44℃
Flow
Natural Source Flow
pH
pH 3.3
0714
AcidicNeutralAlkaline
Use
Stay N/A/Day Trip OK
Fee
Adult 1500JPY/Child ---JPY
Hours
| Mon | Tue | Wed | Thu | Fri | Sat | Sun | Hol | |
|---|---|---|---|---|---|---|---|---|
| 10:00 - 17:00 | ◯ | ◯ | ◯ | × | ◯ | ◯ | ◯ | ◯ |
Founded in 1662, Matsuzakaya Honten is one of Hakone's most distinguished heritage ryokan, immortalized in Utagawa Hiroshige's ukiyo-e woodblock prints. Ashino-yu, at approximately 870 meters elevation, was counted among the "Seven Hot Springs of Hakone" during the Edo period and was designated as Kanagawa Prefecture's first National Health Resort Hot Spring Area in 2015. Its most exceptional quality lies in the rare combination of three "beauty skin" mineral types — sulfur, sulfate, and bicarbonate — all naturally balanced in a single source. Approximately 260 liters per minute well up from just 60 meters below the surface, delivered as 100% source-fed flowing water without any dilution or temperature adjustment. The mystical quality of the water, which changes color with temperature and weather conditions, adds to its allure. Twenty-two rooms spread across six distinct buildings dot the four-thousand-tsubo grounds, creating a serene retreat far removed from Hakone's tourist bustle. With over 360 years of history, the bathing halls offer one of the most authentic hot spring cultural experiences in all of Hakone.
Quality
硫黄泉
Temp
40℃ to 65℃
Flow
Natural Source Flow
pH
pH 7
0714
AcidicNeutralAlkaline
Use
Stay OK/Day Trip N/A
Book your stay
Founded in 1715 during the Shotoku era, Kinokuniya is a venerable ryokan with over 300 years of history in Hakone's Ashino-yu district. The inn was honored as a resting place for Emperor Meiji and has been beloved by literary figures and cultural luminaries throughout its history. Spanning approximately 3,000 tsubo of grounds, the property boasts 15 spring sources and 15 baths of varying sizes, offering two distinct types of natural hot spring water: milky white sulfur springs and clear sodium bicarbonate springs. With a metasilicic acid content of 139 mg, the water is celebrated as a beauty spring.
The main building's Yukoden features sulfur-rich milky waters, while the annex's Kihinden offers crystal-clear bicarbonate spring water. The Shotoku no Yu private bath, available exclusively to overnight guests, faithfully recreates the bathing hall from the inn's founding era. Day-use bathing is also available at a reasonable 1,000 yen for two hours, allowing visitors to experience the tranquil mountain atmosphere unique to Ashino-yu, away from Hakone's tourist crowds.
Quality
単純硫黄泉
Temp
40℃ to 43℃
Flow
Natural Source Flow
pH
pH 7
0714
AcidicNeutralAlkaline
Use
Stay OK/Day Trip OK
Fee
Adult 1000JPY/Child 1000JPY
Hours
| Mon | Tue | Wed | Thu | Fri | Sat | Sun | Hol | |
|---|---|---|---|---|---|---|---|---|
| 15:00 - 10:00 | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ |
Sokokura Onsen is one of the historic Hakone Seven Hot Springs, known since before the Edo period. Kanrei is a distinctive day-use hot spring facility housed in a Western-style building from the Meiji era that once served as a medical clinic. It features a single open-air bath surrounded by bamboo groves along a mountain stream, available in a private reservation style for one-hour sessions. The sodium chloride spring water flows directly from the source, maintaining its natural mineral composition.
With a source temperature of approximately 70°C, the water is adjusted with cold water to a comfortable bathing temperature, producing clear, refreshing water with a gentle touch on the skin. Tucked away from the main thoroughfare of Miyanoshita, the facility offers a peaceful respite far removed from Hakone's tourist bustle. The unique atmosphere created by the Taisho-era retro Western architecture, verdant bamboo groves, and the murmur of the mountain stream has made it a quietly beloved hidden gem among hot spring enthusiasts. Reservations by phone are required before visiting.
Quality
ナトリウム－塩化物泉
Temp
42℃ to 44℃
Flow
Natural Source Flow
pH
pH 7.5
0714
AcidicNeutralAlkaline
Use
Stay N/A/Day Trip OK
Fee
Adult 1500JPY/Child ---JPY
Hours
| Mon | Tue | Wed | Thu | Fri | Sat | Sun | Hol | |
|---|---|---|---|---|---|---|---|---|
| 10:00 - 16:00 | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ |
Summary — What to Know Before Exploring Kanagawa's Hot Springs
The hot springs of Kanagawa Prefecture can be efficiently explored by dividing them into two main areas.
Tanzawa Area: Ao no Sanso and Shingenkan in Nakagawa Onsen, Kabutoyu Onsen Sansuiro, and Iiyama Onsen Motoyu Ryokan are all nestled in the Tanzawa mountain range. The most accessible from Tokyo are Iiyama Onsen Motoyu Ryokan (about 20 minutes from Tomei Atsugi IC) and Kabutoyu Onsen Sansuiro (about 30 minutes from the same IC), both feasible as day trips. The two Nakagawa Onsen inns are located deeper in the Nishi-Tanzawa mountains, making an overnight stay the ideal way to enjoy the early morning baths. A 1-night/2-day itinerary from Iiyama Onsen to Kabutoyu Onsen to Nakagawa Onsen allows visitors to compare the different skin textures of alkaline waters ranging from pH 11.3 down to pH 10.0 — a luxurious bathing tour. Public bus service in the Tanzawa area is limited, so a rental car is recommended. Winter road conditions around Nakagawa Onsen require caution due to potential icing.
Hakone Area: Ubako Onsen Shumeikan, Matsuzakaya Honten and Kinokuniya in Ashino-yu, and Sokokura Onsen Kanrei are all located within Hakone's mountainous interior. Sokokura Onsen Kanrei in the Miyanoshita area offers the easiest access from Hakone-Yumoto. The two Ashino-yu inns sit along Route 1, while Ubako Onsen Shumeikan is conveniently reached by the Hakone Ropeway. Hakone's excellent public transportation network allows visitors to use the Hakone Free Pass to connect mountain railways, cable cars, ropeways, and buses for an efficient circuit. A rewarding day itinerary would be to enjoy day-trip bathing at Kinokuniya in Ashino-yu, then take the ropeway to Ubako for the rare foot-source spring experience at Shumeikan. Matsuzakaya Honten is accommodation-only, so an overnight stay is necessary to savor its 360 years of heritage. During winter (December to February), be aware of potential road icing and snowfall in the Hakone mountains. Note that Shumeikan is closed throughout February and Kanrei operates by reservation only — always confirm before visiting.
The information in this article (admission fees, operating hours, water quality data, etc.) is based on research conducted at the time of writing. Details may have changed or contain errors. Please verify the latest information on each facility's official website or through the local tourism association.
