Echigo-Nagano Onsen RANKEISOU

The spring quality of Rankeisou is classified as Sodium - Chloride cold mineral springs.

Its main components are Sodium Ions (cations) and Chloride Ions (anions). This spring type is commonly known in Japan as a “Hot springs for warmth”. The salt contained in the hot spring water adheres to the skin, forming a thin protective layer that acts like a natural salt pack. This layer helps reduce heat loss by preventing sweat from evaporating too quickly, allowing the body to stay warm long after bathing. For this reason, it is considered beneficial for people with Sensitivity to cold.

In addition, Sodium – Chloride springs help dilate blood vessels and improve blood circulation, making them beneficial for Peripheral circulatory disturbance. Their excellent heat-retaining properties are also believed to help regulate the autonomic nervous system, contributing to the improvement of Depression.

This spring is also known as “Hot springs for cuts” because its salt content has bactericidal properties, making it beneficial for Cuts.

The combination of sodium and chloride ions provides a moisturizing effect, helping to lock moisture into the skin and making it beneficial for people with Dry skin.

(*Text in blue indicates Indications for bathing in this spring quality)

Compared with the many hot springs found throughout Japan, the spring at Rankeisou is truly exceptional.

One of the main reasons is its remarkably high concentration of dissolved substances.

According to the official Hot Spring Analysis, the total amount of dissolved substances is 8,739 mg/kg!

Under Japan's Hot Springs Act, one of the criteria for qualifying as a therapeutic hot spring is a total dissolved substance content of 1,000 mg/kg or more (excluding gaseous substances). At 8,739 mg/kg, Rankeisou's spring contains more than 8 times the required minimum.

In other words, it is an exceptionally “highly” concentrated hot spring, a rarity even by Japanese standards.

For comparison, the famous Yubatake Source at Kusatsu Onsen contains approximately 1,780 mg/kg of dissolved substances.

Even this renowned hot spring has only about one-fifth of the dissolved substance content found at Rankeisou, highlighting just how extraordinary this spring truly is.

Further evidence of Rankeisou's exceptional character can be found in its Osmotic pressure, one of the indicators used to classify Japanese hot springs.

In simple terms, osmotic pressure indicates how readily hot spring minerals can be absorbed by the body during bathing.

It is classified into three categories based on osmotic pressure: hypotonic, isotonic, and hypertonic.

Isotonic hot springs have a mineral concentration similar to that of human body fluids, which is roughly equivalent to a saline solution containing 8.8 g of salt dissolved in 1 liter of water.

Hot springs with a lower mineral concentration are classified as hypotonic, while those with a higher concentration are classified as hypertonic.

In general, hot springs with less than 8,000 mg/kg of total dissolved substances are classified as hypotonic, those containing 8,000–9,999 mg/kg are isotonic, and those with 10,000 mg/kg or more are hypertonic.

In fact, the vast majority of hot springs in Japan are hypotonic, containing less than 8,000 mg/kg of dissolved substances.

Osmotic pressure is the natural tendency of water to move from an area of lower solute concentration to one of higher solute concentration through a semipermeable membrane.

In hypotonic hot springs, water tends to move into the body more readily, while hot spring minerals are generally less readily absorbed.

In hypertonic hot springs, water tends to move out of the body more readily, while hot spring minerals are more readily absorbed.

As a result, hypertonic hot springs tend to have stronger physiological effects. Because they are more physically demanding, bathers should take care to avoid hot spring fatigue (yu-atari).

With a total dissolved substance content of 8,739 mg/kg, the spring at Rankeisou is classified as Isotonic, making it a rare and highly concentrated hot spring in Japan.

In other words, because its mineral concentration is relatively close to that of human body fluids, there is less movement of water and dissolved minerals across the skin. As a result, the effects of osmotic pressure are relatively moderate.

However, compared with commercially available bath additives, Rankeisou's spring contains approximately 58 to 87 times more active mineral components!

This comparison is based on adding one standard dose of a bath additive (assuming 100–150 mg/kg of artificial active ingredients) to a typical household bathtub containing approximately 200 liters of water.

The spring water is clear and colorless, but its mineral content is anything but ordinary.

Next, let's look at the spring temperature. The source at Rankeisou emerges at a relatively cool 15°C.

In Japan, springs with a temperature of 25°C or higher are classified as “Hot springs”, while those below 25°C are classified as “Cold mineral spring”.

The relatively low spring temperature also suggests that this is a non-volcanic hot spring.

While many of Japan's hot springs are volcanic in origin, with heat supplied by magma, Rankeisou's spring is believed to originate from “fossil seawater”—ancient seawater that became trapped underground by crustal movements millions of years ago. Although several theories exist, this is the most widely accepted explanation.

The spring water is pumped from a depth of approximately 100 meters below ground. As it passes through underground rock layers, it dissolves a rich variety of minerals, giving the spring its distinctive mineral composition.

Although the spring water is heated to a comfortable bathing temperature, its mineral composition is virtually unaffected.

Next, let's look at the pH level. With a pH of 7.9, Rankeisou's spring is classified as Weakly alkaline.

Weakly alkaline hot springs help soften and remove dead skin cells from the skin's surface, leaving the skin feeling smooth and silky.

For this reason, they are often referred to in Japan as “Hot springs for beautiful skin”.

Another noteworthy feature is its high hydrogen carbonate ion content of 1,191 mg/kg. Although this does not appear in the official spring classification, it is also present in a remarkably high concentration.

Hydrogen carbonate ions help emulsify and wash away excess sebum and dead skin cells from the skin's surface, providing a gentle cleansing effect and leaving the skin feeling softer and smoother.

The official spring classification is “Sodium – Chloride cold mineral springs”, rather than Sodium- Hydrogen carbonate springs, despite the high hydrogen carbonate ion content. This is because Japan's hot spring classification follows the 20% rule.

Under this rule, when the total dissolved substances (excluding gaseous) are 1,000 mg/kg or more, only ions accounting for more than 20% of the total milliequivalents (mval%) are used in the official spring classification.

The mval% (milliequivalent percentage) represents the proportion each ion contributes to the total milliequivalents of all dissolved ions. It is the standard used to determine the principal components of a hot spring.

At Rankeisou, sodium ions account for 2,957 mg/kg (93.39 mval%) of the total cations, while chloride ions account for 4,322 mg/kg (85.60 mval%) of the total anions.

Because these two ions each exceed 80% of their respective ion groups, hydrogen carbonate ions, despite being present at 1,191 mg/kg (13.71 mval%), are not reflected in the official spring classification.

For comparison, one of Japan's best-known “Hot springs for beautiful skin”, Ureshino Onsen in Saga Prefecture, classified as a Sodium – Hydrogen Carbonate / Chloride springs, contains approximately 930 mg/kg of hydrogen carbonate ions.

Likewise, Higashi-Naruko Onsen in Miyagi Prefecture, a Sodium – Hydrogen carbonate springs, contains 556 mg/kg of hydrogen carbonate ions.

By comparison, Rankeisou contains an impressive 1,191 mg/kg of hydrogen carbonate ions. Although this exceeds the levels found in these famous hot springs, it cannot officially be classified as Hydrogen carbonate springs, the spring type most closely associated with Japan's famous “Hot springs for beautiful skin”, because of Japan's 20% classification rule.

In terms of its actual mineral composition, however, it possesses many of the characteristics commonly associated with hydrogen carbonate springs.

Hydrogen carbonate ions also combine with sodium ions to form sodium hydrogen carbonate (baking soda).

In Japan, a concentration of 340 mg/kg or more of sodium hydrogen carbonate qualifies as one of the standards for therapeutic hot springs. Rankeisou contains 1,639.8 mg/kg—approximately 4.8 times the required standard.

Like hydrogen carbonate ions, sodium hydrogen carbonate helps emulsify excess sebum and dead skin cells on the skin's surface, allowing them to be washed away like soap.

As a result, it leaves the skin feeling smooth and silky after bathing and is widely recognized as one of the key mineral components of Japan's “Hot springs for beautiful skin”.

The combination of weakly alkaline water and hydrogen carbonate ions (sodium hydrogen carbonate) helps leave the skin feeling smooth and silky after bathing. In this sense, Rankeisou can truly be called “Double Hot springs for beautiful skin”.

However, even hot springs renowned for their skin-beautifying properties have one potential drawback.

The cleansing action of weakly alkaline water and hydrogen carbonate ions can temporarily leave the skin more prone to dryness by removing excess sebum along with dead skin cells.

In most cases, applying a moisturizer after bathing is recommended. However, it is important to remember that Rankeisou's spring is also rich in salt.

As mentioned earlier, the salt forms a thin protective layer on the skin after bathing, helping to lock in moisture and reduce dryness.

In other words, the spring not only cleanses the skin and leaves it feeling smoother, but also helps maintain moisture afterward.

Rankeisou's spring offers the best of both worlds: it gently removes dead skin cells for smoother skin, then helps lock in moisture with a natural salt coating.

Another noteworthy non-dissociated component is Metaboric acid, which is present at 22.7 mg/kg.

Since the qualifying standard for therapeutic hot springs is 5 mg/kg, Rankeisou contains approximately 4.5 times the qualifying standard.

Metaboric acid is believed to have cleansing properties at concentrations above 10 mg/kg and is said to help prevent acne.

To help conserve this valuable hot spring resource and because the spring's yield is limited, Rankeisou continuously introduces fresh spring water while circulating the water within the baths. However, only natural spring water is used—no additional water is added.

Some people may worry that heating or circulation reduces the quality of the spring water. However, the principal mineral components in Rankeisou's spring are highly stable and are not easily affected by heating or circulation, allowing guests to enjoy the spring's natural benefits.

In many circulating hot springs, chlorine is routinely used for disinfection. At Rankeisou, however, chlorine use is kept to the absolute minimum, except for periodic disinfection measures carried out to prevent Legionella contamination.

Given the spring's exceptionally high salt content and its natural bactericidal properties, one might even wonder whether chemical disinfection would be necessary at all. Nevertheless, appropriate hygiene management remains essential to ensure guest safety.

The spring at Rankeisou, a secluded inn in Echigo-Nagano Onsen, Niigata Prefecture, comes from a private source.

In the early Showa era (1926–1989), this spring water was reportedly sold as a medicinal remedy.

It truly deserves to be called a “medicinal spring”, and it is easy to imagine how impressed people must have been by its remarkable properties when the inn first opened.

Guests can also enjoy drinking the spring water at the traditional irori (sunken hearth) in the lobby.

Although the spring water is salty, it has a rich, savory flavor reminiscent of kombu tea.

Guests are also served roasted green tea (hojicha) brewed with the spring water.

At breakfast, the inn's signature rice porridge is prepared using the spring water. Despite its unusual ingredient, it is surprisingly delicious.

This is likely because the spring water is blended with fresh spring water known as “Maki-no-Shimizu” to achieve a pleasant level of salinity.

Combined with its abundance of naturally occurring minerals, the result is a rich, well-balanced flavor unlike that of ordinary mineral water.

The Indications for drinking chloride spring water include Atrophic gastritis and Constipation.

Sodium chloride helps stimulate the gastric mucosa, promoting the secretion of gastric acid while also helping to protect the stomach lining.

It also stimulates the intestinal walls, encouraging peristalsis and allowing waste to pass more smoothly through the intestines.

Whether soaking in the baths or enjoying the spring water, Rankeisou offers a unique opportunity to refresh both body and mind from the inside and out.

Nestled in the mountains of Nagano, Sanjo city, in the Chuetsu region in Niigata Prefecture, near the border with Fukushima, “Rankeisou” is the only ryokan in the hot spring area known as Echigo-Nagano Onsen.
No wonder it has such a timeless appearance. It was originally built as a ryokan in front of Tsubame Station during the early Showa period (the late 1920s to early 1930s), the building was relocated to its current location around 1955. Today, it serves as “Ryokufuukan”, the main building and reception area of Rankeisou.
This three-story wooden building has a timeless presence, quietly preserving the stories of the many people who have been connected to it throughout the years. It exudes a quiet dignity. In 2012, Ryokufuukan was designated a Registered Tangible Cultural Property of Japan, in recognition of its historical and architectural value.

Rankeisou has long been renowned for its exceptional therapeutic hot spring, once celebrated as a “medicinal spring”.
The term “medicinal spring” is used intentionally because, during the early Showa period, the hot spring water was actually sold at a pharmacy in Tokyo's Hatchobori district as a remedy for burns.
The spring water contains an extraordinarily high concentration of salt. This unusually high salinity was believed to provide bactericidal properties, making it highly valued for its healing effects.
The story of this private spring source began in the late Taisho period (around 1924–1926), when the founder, Yasukichi Otake, discovered the spring. Inspired by its remarkable qualities, he opened as a therapeutic bathing facility in 1927 (Showa 2), laying the foundation for what is now Rankeisou.

Today, Rankeisou offers a total of 16 guest rooms (as of 2026), spread across three distinctive buildings.
The first is “Ryokufuukan”, the main building and reception area, which has been designated as a Registered Tangible Cultural Property of Japan.
The second is “Keiryukan”, a guest room wing built in 1992.
The third is “Suiyukan”, a guest room wing with Western-style beds, renovated in November 2022. It was created by refurbishing “Rindokan”, a building originally constructed in the early 1960s and extensively renovated in 2001.

“Ryokufuukan” originally featured guest rooms without private bathrooms or toilets. Following renovations completed in 2025, two of the rooms were equipped with private toilets. With its warm wooden architecture and evokes the charm of traditional Japan, this building remains a favorite among returning guests. (5 rooms)
“Keiryukan” offers traditional Japanese-style rooms with private bathrooms and toilets, making it the main guest room wing of Rankeisou. Each room features a large picture window overlooking the scenic mountain valley and the Sumon River. (8 rooms)
The guest rooms in “Suiyukan” (formerly Rindokan) feature tatami flooring with Western-style beds, making them ideal for guests of all ages, from young children to seniors. The private open-air bath “Yama-no-Yu” is conveniently located right next to the building.
Each room is also equipped with a spacious desk suitable for remote work, as well as both Wi-Fi and wired LAN access. With its open terrace and work-friendly environment, “Suiyukan” is an excellent choice for guests planning an extended stay or a workation. (3 rooms)

The surrounding natural landscape invites guests to enjoy a leisurely stroll.
In summer, children can often be seen playing in the clear waters of the Sumon River, which flows right in front of the inn. This crystal-clear mountain stream is also home to iwana (Japanese char) and ayu (sweetfish), making it a popular spot for guests who enjoy fishing.
An outdoor table tennis area is also available, offering a refreshing way to relax and enjoy a bit of exercise while surrounded by the fresh mountain air.

Rankeisou offers something special in every season.
In spring, guests can enjoy the delicate beauty of Himesayuri lilies, wildflowers, and cherry blossoms. Soaking in the hot spring while surrounded by fresh greenery and the sound of snowmelt-fed streams is a truly luxurious experience.
Summer brings a magical atmosphere as fireflies dance above the irrigation canal beside the inn, where a traditional waterwheel slowly turns. The cool breeze from the mountain stream provides a welcome escape from the heat.
In autumn, the surrounding landscape is transformed by vibrant fall colors, creating breathtaking scenery in every direction.
Winter turns the area into a fantastical world of snow, characteristic of one of Japan's heaviest snowfall regions. Guests can enjoy a relaxing “yukimi-buro” (snow-viewing bath) while soaking in the hot spring. From February to mid-March, guests can also enjoy playing in traditional kamakura snow huts. Squirrels and Japanese giant flying squirrels are also frequently seen in the area.

The cuisine at Rankeisou changes with the seasons, featuring the freshest local ingredients, including wild mountain vegetables, freshwater fish, and vegetables harvested at their peak.
Prepared with fresh mountain spring water, these wholesome dishes showcase the rich bounty of the surrounding mountains and countryside, creating a memorable dining experience that has inspired many guests to return time and again.

Rankeisou reflects a philosophy of preserving its heritage while embracing modern comfort.
Nearby stands Yagigahana, a striking rock formation where peregrine falcons return each year to nest. In spring, visitors may even witness the parent birds raising their chicks.
For those leading busy lives in the city, knowing there is a secluded hot spring inn nestled in the heart of nature like this is enough to make you want to escape here whenever you need a break.
Travel Journal