CHIGIRA JINSENTEI

In Gunma Prefecture, there are 3 excellent hot spring resorts known as the “Three Famous Hot Springs of Joshu” —Kusatsu, Ikaho, and Shima. Among them, Ikaho Onsen is especially well-known for its reddish-brown colored hot spring called “Kogane-no-Yu” (Golden Hot Spring). Located nearly in the center of Gunma Prefecture, Ikaho Onsen is situated at an elevation of 700 to 800 meters on the northeastern slope of Mount Haruna. It is believed that the hot spring emerged as a result of the eruption of Mount Futatsudake in the 6th century. In the Manyoshu, Japan’s oldest anthology of poetry compiled between the late 7th and late 8th centuries, several poems mention the name Ikaho.

The source of Kogane-no-Yu can be found further beyond the top of the Ishidan-gai (Ikaho stone steps), in an area where the Ikaho Open-air Bath is located. The hot spring is drawn from wells drilled 100 to 400 meters underground, mixed, and flows at a rate of 4,627 liters per minute. The water is delivered through wooden channels beneath the stone steps to 9 inns that hold rights to use this water. One of those inns is Chigira Jinsentei. Near the spring source outlet, you can see the stone wall of the “Site of the Original Chigira Residence”, a registered historical landmark in Shibukawa City, Gunma Prefecture. The Chigira family, a powerful clan, managed the spring, and it is believed that an inn existed near this location as early as 1502, which is considered the founding of Ikaho Onsen. Long ago, hot springs served as a kind of medical treatment facility. After the defeat at the Battle of Nagashino in 1575, Takeda Katsuyori ordered Sanada Masayuki to develop the spring to heal his soldiers, which is how the famous stone steps came into being. Inns were built along the slope using the natural incline, with the source at the top. Other influential clans also settled in the area and opened inns along the steps.

Chigira Jinsentei, being the first inn of Ikaho and once the sole owner of the spring source, currently holds the most abundant rights among the 9 inns using Kogane-no-Yu. Every bath in the facility is filled with 100% natural free-flowing hot spring water, without any added water, circulation, or disinfection. The color of the water is colorless and clear when it emerges, but it turns its mystical brown shade as the iron content oxidizes upon exposure to air. The famous brown-colored Japanese sweet, “onsen manju” (hot spring buns), often associated with hot spring resorts, derives its coloring from this spring.

Today, there are fewer than 50 hot spring inns in Ikaho, but only a limited number hold the rights to Kogane-no-Yu. Because of this, many inns have insufficient water supply and must receive water from inns that hold the rights. In 1996, Shibukawa City successfully drilled a new spring called “Shirogane-no-Yu” (Silver Spring). Unlike Kogane-no-Yu, it is colorless and does not meet the 25℃ requirement for named spring classification, though it is officially recognized under the Hot Spring Act due to its metasilicic acid content.

The spring quality of Kogane-no-Yu is classified as a “Calcium, SodiumSulfate / Hydrogen Carbonate / Chloride spring”. In short, it has the 3 characteristics of sulfate, hydrogen carbonate, and chloride springs. The pH value is 6.4, which is neutral and thus gentle on the skin, making it safe and comfortable for everyone from children to the elderly. There are many common indications for spring quality. The therapeutic benefits of the spring types—“sulfate springs”,“hydrogen carbonate springs”, and “chloride springs”—are largely shared. They are effective for cuts, peripheral circulatory disturbance, sensitivity to cold, and dry skin. The thermal effects of sulfate and chloride springs also influence the autonomic nervous system and are said to be effective for depression.

Among the dissolved substances, calcium ions (a cation) and sulfate ions (an anion) are the most abundant, forming a “Calcium Sulfate Spring”. In the old classification, this was called a “gypsum spring”. Sulfate ions have healing effects on wounds and also stimulate skin elasticity, helping prevent wrinkles. Hence, this spring is known both as a “Hot springs for cuts” and an “Hot springs for anti-aging effect”. Calcium ions help form the skin’s keratin layer, making it famous as a “Hot springs for beautiful skin”. Moreover, due to its calming properties, it is also called a “Hot springs for strokes”.

The second most abundant anion is the hydrogen carbonate ion, which enhances blood circulation. When combined with calcium or magnesium ions, it forms a “Calcium (or Magnesium) Hydrogen Carbonate spring”, previously classified as a “bicarbonate earth spring”. In the new classification, hydrogen carbonate springs include both the old “bicarbonate earth spring” and “sodium bicarbonate spring” (baking soda spring). Calcium Hydrogen Carbonate Springs (bicarbonate earth spring) often contain carbon dioxide and iron, and have a calming effect due to calcium and magnesium ions. They are also effective for chronic skin diseases and allergic dermatitis. Like sulfate springs, hydrogen carbonate springs are known as “Hot springs for beautiful skin”. Additionally, hydrogen carbonate springs promote perspiration after bathing, giving a refreshing post-bath sensation, which makes them popular even in the summer—hence the nickname “Hot springs for refreshing (with cooling effect)”.

The third major component, chloride ions (anions), helps retain body heat. The so-called “Sodium Chloride spring” (formerly “salt spring”) prevents rapid cooling after a bath by blocking sweat glands with salt, hence called a “Hot springs for warmth”. Moreover, the coating effect of the salt in chloride springs contributes to their high moisturizing properties.

As evidenced by its diverse therapeutic benefits, Kogane-no-Yu is an exceptional hot spring. Moreover, it is 100% natural, flowing directly from the source without added water or circulation—truly a gift for the body. Chigira Jinsentei uses approximately 400 to 800 liters per minute (depending on seasonal variations in output) from “Kogane-no-Yu”(total spring output: 4,670 L/min). Since the source temperature is 41.6℃, the water may cool slightly before reaching the baths, requiring heating during cooler months. This heating has minimal impact on the spring’s quality.

Also noteworthy are the sodium and hydrogen carbonate ions. According to the “Guidelines for the Mineral Spring Analysis Methods”, sodium-hydrogen carbonate (sodium bicarbonate) is considered a mineral salt. The guideline recommends multiplying the lesser of the two mval/kg values by the molecular weight (84.01) of sodium hydrogen carbonate. According to the spring analysis, sodium ions are 4.41 mval/kg. Thus, 4.41 × 84.01 = 370.48 mg/kg, exceeding the required 340 mg/kg for hot spring qualification.

Metasilicic acid, a natural moisturizing component, is also present at over 3 times the qualifying standard, contributing to soft, moisturized skin—another reason this spring is classified as a “Hot springs for beautiful skin”. Furthermore, metaboric acid, known for acne prevention and cleansing, also exceeds the standard.

As a sub-specific feature, the spring contains 7.23 mg/kg of ferro ions (Fe2+), just below the 10 mg/kg requirement for official recognition but still beneficial. It promotes warmth, and may help with anemia, menopausal disorders, and menstrual issues. "Kogane-no-Yu" has long been referred to as a “Hot springs for fertility”," possibly due to these effects. Another significant element is the 172 mg/kg of free carbon dioxide. While 250 mg/kg is required for hot spring status and 1,000 mg/kg for a recognized carbonated spring, this amount still exceeds most commercial bath additives, which contain only 40–100 mg/kg. However, due to the high temperature of the spring, bubbles are not visible.

Though the spring water has recognized benefits for drinking—such as for biliary dysfunction, hypercholesterolemia, constipation, gastroduodenal ulcers, reflux esophagitis, impaired glucose tolerance (diabetes), hyperuricemia (gout) and atrophic gastritis—the inn currently does not have public health approval for drinking use.

Despite having an abundance of hot spring water, Chigira Jinsentei has only 33 guest rooms with a maximum capacity of 130 guests. With 400 to 800 liters of hot spring water per minute, the inn could easily double its capacity while still maintaining 100% natural flow to all baths. However, the inn has deliberately chosen to remain at this scale. Could this be a reflection of its deep sense of responsibility as the founding ryokan of Ikaho Onsen? Its sincere commitment to cherishing the hot spring—an invaluable gift from the earth—has supported its operation for over 500 years. The long-standing history is proof of this enduring devotion.

Ikaho Onsen is one of the most popular hot spring areas in the Kanto region, located halfway up Mt. Haruna in Gunma Prefecture, and has a rich history and tradition from the Manyo Period (710-794). It is said that the hot spring water was discovered either 1,900 or 1,300 years ago. "Chigira Jinsentei", established over 500 years ago, is one of the oldest ryokan in the Ikaho Onsen area. The symbol of Ikaho is the 365-step Ishidan Street (stone stairway). When you climb to the top of the stone steps, near the Kawaga Bridge, you will find the source of the Ikaho Onsen "Kogane-no-Yu", and next to it, surrounded by stone walls, is the site of the "Chigira Motoyashiki". During the Tenbun era (1532-1555) of the Sengoku period, when Uesugi Norimasa, the nominal Kanto governor, was ruling the area, the Chigira clan was already in charge of the hot spring source. In the Edo period (1603-1867), the "Komaguchi Right Holders Association" was created to own the rights to the hot springs, which continues to this day, and the "Chigira Jinsentei" continued to be a central member of the association. The "Komaguchi Right Holders" (source owners) means those who own "Komaguchi", which is a hot spring piping system, and who each own a certain amount of hot spring water. Today, the 9 owners of the ryokan have formed an association to protect the centuries-old reddish brown "Kogane-no-Yu" (golden water) by stipulating strict rules for its use. Of these 9 ryokan, "Chigira Jinsentei" is said to have the largest amount of hot spring water per guest. Today, "Chigira Jinsentei" stands halfway up the stone staircase street and is also an inn connected to Tokutomi Roka (1868-1927), a great writer of the Meiji and Taisho eras. Roka loved Ikaho, especially this "Chigira Jinsentei" inn, and stayed here regularly, and even passed away here. His masterpiece, "Fujoki (The Cuckoo)" which is based on this inn was also set in this inn. Also, the poet Akiko Yosano and the great writer Junichiro Tanizaki are known to have visited the inn. Today, the inn is also known as the Imperial Family's official lodging. Despite its history and traditions, the inn is supported by a wide range of customers, with rooms available at reasonable rates, as well as rooms with the popular open-air bath. The inn has a large number of baths: large public baths for men and women + indoor baths, large public baths for men and women (Ninoyu and Takiyu), and 4 private baths that can be used free of charge. And the most wonderful thing about this inn is that the "Kogane-no-Yu" (golden water) is so abundant than other inns envy, and can be experienced as 100% natural free-flowing hot spring water. At present, there are around 50 onsen ryokan in Ikaho Onsen, but it is said that only about half of them use "Kogane-no-yu" (golden water). 9 of the right holders (source owners) must be splitting the hot spring with them. Note that "Chigira Jinsentei" does not share its hot spring water with any other ryokan. A regular customer told us that the hot springs here are "richer" than anywhere else. (Jin)
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