Shima Onsen is a quiet hot spring area in the mountains of Nakanojo Town, Agatsuma District, Gunma Prefecture, known for the clear blue water of the Shima River and Oku-Shima Lake, called "Shima Blue," and for Sekizenkan, a retro wooden hot spring inn that symbolizes the area. Unlike bustling entertainment districts, it has a calm, old-style therapeutic atmosphere with inns scattered along the river, making it ideal for travelers seeking tranquility and scenery rather than noise. Its history as the first designated national health resort hot spring area in 1954 also reflects the character of this destination.

For visitors, the key appeal of Shima Onsen lies in three elements: the quiet valley scenery of Shima Blue, the atmosphere of old hot spring inn architecture at Sekizenkan, and its long history as a therapeutic bathing area. The spring water itself is colorless and gentle, so this is a hot spring area to enjoy through the calm of the town, the beauty of the water, and the architecture rather than flashy visuals. This article organizes the history of Shima Onsen, Shima Blue, Sekizenkan, the spring quality and drinking water culture, sightseeing routes, and access, based on information from the Shima Onsen Association and Nakanojo Town.

What kind of hot spring area is Shima Onsen?

Shima Onsen is a hot spring area in the mountains along the Shima River in Nakanojo Town, northwestern Gunma Prefecture. Its name is said to come from the legend that it can heal "40,000 illnesses," though there are several theories about the origin and it cannot be stated with certainty. In any case, it has long been known as a therapeutic hot spring area, and unlike large entertainment-style resorts such as Kusatsu Onsen, it is characterized by a quiet layout with inns scattered along the river.

This tranquility is officially reflected in the fact that in 1954 it was designated by the then Ministry of Health and Welfare, now the Ministry of the Environment, as the first national health resort hot spring area. The national health resort hot spring system is a government designation based on factors such as spring quality, environment, and suitability for therapeutic use. Shima Onsen is known as one of the first sites to receive this designation. If you understand it as a hot spring area that values peaceful time with nature and the water itself more than lively entertainment, your impression on site will match the reality more closely.

The hot spring town stretches long and narrow along the Shima River, and is divided into areas such as Onsen-guchi, Arayu, Yuzuriha, and Hinatami. Each area has different inns and a different atmosphere, so your experience changes depending on where you stay and where you walk. It is easier to explore if you first grasp the overall image of a calm riverside town and then move around from there.

What is Shima Blue?

One of the essential features of Shima Onsen is the clear blue color seen in the Shima River and Oku-Shima Lake, commonly called "Shima Blue." Depending on the light, season, and weather, the color is said to shift from emerald green to deep blue, and the water surface on a sunny day is often described as especially striking. However, because the appearance changes greatly depending on conditions, it is best to treat this as a guide rather than expect the same blue every time.

The most representative place to see Shima Blue is Oku-Shima Lake, a reservoir upstream from the hot spring town. From lakeside paths and observation points, you can view the blue water surface, and in the seasons of fresh greenery and autumn leaves, the colors of the water and the mountains overlap beautifully. Along the Shima River flowing through the hot spring town, you can also find the same blue tint in pools and currents. If your main goal is the water color, visiting during daylight when the light is easy to catch makes it easier to appreciate.

The reason the water appears blue is said to involve several factors, including the scattering of light by fine particles in the water, but there is no single established explanation. If you are interested in why hot springs and water can appear blue in general, see Blue-Colored Hot Springs as well. Note that Shima Blue refers to the color of the river and lake water, not the color of the hot spring water itself.

Sekizenkan and retro hot spring inn architecture

The architectural symbol of Shima Onsen is Sekizenkan in the Arayu area. The main building of Sekizenkan is said to date back to 1694 in the Genroku period, and it is often introduced as one of Japan's oldest wooden hot spring inn buildings. However, the question of whether it is truly the "oldest" varies depending on the source, and the construction year and evaluation differ from one reference to another, so it is best to regard this as a guide. In addition to the old main building, there are buildings from the early Showa period and modern wings connected together, making the blend of different eras one of the highlights.

In front of Sekizenkan is Keiunbashi, a vermilion bridge over the Shima River, and the sight of the red bridge beside the wooden buildings is known as one of the signature landscapes of Shima Onsen. Because of this atmosphere, it is sometimes rumored to have inspired the world of the animated film Spirited Away, but this has not been officially confirmed. Since the creators have not clearly stated that any specific building was the model, it should be understood only as an unofficial claim that is sometimes mentioned.

Another feature of Shima Onsen is that the buildings and architecture themselves can be part of the trip. The design of the old hot spring inn and the layered history of the structures are part of the value of the scenery, and there is enjoyment not only in bathing but also in walking around and looking at the buildings. If you are interested in hot spring architecture and how design shapes the experience, see Hot Spring Architecture and Design. Sekizenkan is an active inn, so whether and how much of it can be toured depends on the facility's guidance.

Spring quality and the "stomach and intestines bath"

The spring water of Shima Onsen is often introduced as a sodium-calcium chloride-sulfate spring. It is a mixed spring containing both chloride and sulfate ions, and the water is colorless, clear, and gentle. It does not have the strong acidity of Kusatsu or the distinctive white turbidity and smell of sulfur springs, so it is easier to understand as a spring to enjoy for its bathing comfort rather than its appearance. If you want to know the exact spring quality, the most reliable method is to check the hot spring analysis certificate posted at each facility.

Shima Onsen has long been called the "stomach and intestines bath," but this is only a traditional nickname and this article does not claim any medical effect. The tendencies traditionally associated with chloride springs and sulfate springs are summarized in Chloride Springs and What Is a Sulfate Spring?. If you want to first understand the overall picture of the 10 spring types, start with Hot Spring Spring Types for Beginners, which makes the position of Shima's water easier to understand.

Shima Onsen is also said to have places where drinking the spring water is possible. Because of the nickname "stomach and intestines bath," drinking spring water often attracts attention, but it must only be done at facilities or drinking-water stations where it is explicitly permitted. Not all sources are drinkable, and there are limits on quantity and frequency, so do not casually taste the source water while sightseeing; always follow local instructions. The cultural background of drinking hot spring water is summarized in The Culture of Drinking Hot Spring Water.

How to tour the sights

In Shima Onsen, baths, scenery, architecture, and history are spread along the river. Because the sites are spread out, it is easier to get around if you decide in advance what area to use as your base. Here is a quick guide to the main sights.

Sekizenkan and Keiunbashi are concentrated in the Arayu area, so if you want to quickly capture the classic scenery of Shima Onsen, this is the most straightforward place to start. If you want to see Shima Blue properly, you need to go farther upstream to Oku-Shima Lake, and it is best to allow enough time for lakeside walks and viewpoints. Since the distance is too great to do entirely on foot, it is easier to combine transportation such as a car, hotel shuttle, or local bus.

If you want to enjoy the history and quiet atmosphere, the area around the old Yakushi hall in the Hinatami district is also known as a calm spot. Along the river there are public bathhouses and foot baths, so you can enjoy the water in the middle of a town walk. If you want to enjoy an open-air bath integrated with the scenery, see Open-Air Baths in Nature. This is a destination that makes it easy to create a trip focused on quietly enjoying water, architecture, and baths while walking, rather than on lively sightseeing.

Access and how to plan your stay

Shima Onsen cannot be reached by train alone; you also need a bus from the nearest station. If you are traveling by train, Nakanojo Station on the JR Agatsuma Line is the gateway, and from there the local bus to Shima Onsen takes about 40 minutes. Travel time, frequency, and the last bus vary by season and timetable, so it is wise to check the official information before your visit. If you go by car, you have more freedom and it is easier to visit distant sights such as Oku-Shima Lake, but because the roads are in the mountains, you must prepare for snow and freezing in winter.

On site, the sights are scattered along the river, and there is also distance between the hot spring town and Oku-Shima Lake. Trying to visit everything on foot takes time, so it is more realistic to divide your plan into areas you will cover on foot and areas you will visit by bus or car, using your accommodation as the base. Since this is a quiet hot spring area, nights become calm early, so instead of expecting nightlife, it is better suited to enjoying the scenery and architecture during the day and relaxing at the inn.

For an overnight stay, a good plan is to walk around Sekizenkan and the hot spring town on arrival day to get a feel for the atmosphere, then visit Oku-Shima Lake for Shima Blue and the Hinatami area the next day. If you are looking for accommodations or day-use bathing facilities in Shima Onsen and the surrounding area, we provide Facility Listings and a Search Page so you can filter by area and budget. It is also easy to combine this trip with other famous Gunma hot springs such as Kusatsu and Ikaho, and Top 10 Famous Hot Springs in Japan is useful for understanding how they compare.

Seasonal highlights

Shima Onsen changes appearance with the seasons. In spring, the combination of fresh greenery and Shima Blue is vivid, making it an easy season for focusing on the color of the water. In autumn, the scenery of the leaves, river, and lake overlaps, and the changing colors around Oku-Shima Lake become a highlight. The best viewing period varies by year and climate, so if scenery is your priority, check the latest information before you go.

Winter brings snowy scenery and the quietness of the river, but because it is in the mountains, travel becomes more difficult due to snow and icy roads. If you are driving, do not forget to check your tires and the weather, and if you are using public transportation, be sure to check bus frequency and the last departure in advance. Since this is a hot spring area in the mountains at some altitude, it is reassuring to bring one extra layer regardless of the season. No matter the season, the quiet character of Shima Onsen remains the same.

FAQ

Can you see Shima Blue at any time?

Shima Blue is the blue color seen in the water of the Shima River and Oku-Shima Lake, and the shade is said to change depending on light, season, and weather. It is often described as especially beautiful on sunny daytime, but the appearance changes greatly depending on conditions, so the same blue is not guaranteed every time. If your main purpose is the water color, it is easier to appreciate during a time of day when the light is favorable.

Is Sekizenkan really the model for Spirited Away?

Because of the appearance of Sekizenkan and the vermilion Keiunbashi bridge, people sometimes say it inspired the world of Spirited Away, but this has not been officially confirmed. The creators have not explicitly stated that any specific building was the model, so it is best to treat this as an unofficial story. The old atmosphere of the architecture itself is one of Shima Onsen's attractions.

What kind of water can you bathe in at Shima Onsen?

The spring is often introduced as a sodium-calcium chloride-sulfate spring, and the water is colorless, clear, and gentle. It does not have the strong acidity of Kusatsu or the cloudy sulfur smell that stands out, so it is a spring to enjoy for bathing comfort. If you want to know for sure, check the hot spring analysis certificate posted at each facility. The nickname "stomach and intestines bath" is traditional and does not guarantee any effect.

Can you drink the hot spring water in Shima Onsen?

There are said to be places where drinking the spring water is possible, but this can only be done at facilities or drinking-water stations that explicitly allow it. Not all sources are drinkable, and there are limits on quantity and frequency, so always follow local instructions. The cultural background of drinking hot spring water is summarized in The Culture of Drinking Hot Spring Water.

How do you get to Shima Onsen?

It cannot be reached by train alone; a bus is needed at the end. Take the train to Nakanojo Station on the JR Agatsuma Line, then ride the local bus to Shima Onsen for about 40 minutes. Travel time, frequency, and the last bus vary by season and timetable, so it is reassuring to check official information before visiting. If you go by car, it is easier to visit distant sights such as Oku-Shima Lake, but in winter you need to prepare for snow and icy roads.

Conclusion

Shima Onsen is a quiet famous hot spring area in Nakanojo Town, Gunma Prefecture, symbolized by the clear blue Shima Blue and Sekizenkan, a wooden hot spring inn building said to be among Japan's oldest. It was designated in 1954 as the first national health resort hot spring area and still preserves the calm atmosphere of a therapeutic bathing area with inns scattered along the river. The spring water is a colorless, gentle sodium-calcium chloride-sulfate spring, so this is a hot spring area to enjoy through water, architecture, and quietness rather than flashy visuals.

For first-time visitors, a good flow is to start around Sekizenkan to grasp the classic scenery of Shima Onsen, then head to Oku-Shima Lake to see Shima Blue, and walk along the river within a reasonable range. Because there are several theories and unofficial stories about the appearance of Shima Blue, the Sekizenkan model theory, and the origin of the hot spring, it is best to treat them as guides and simply enjoy the quiet environment and the scenery itself, which is the most suitable way to experience this hot spring area.

Sources

• Shima Onsen Association (Nakanojo Town Tourism Association)
• Shima Onsen Official Site
• Nakanojo Town
• Ministry of the Environment, "Guidelines for Mineral Spring Analysis Methods (Revised 2014)"