Sapporo's Secret Onsen Sanctuary
Marukoma Onsen Ryokan

Marukoma Onsen Ryokan is a secret hot spring inn located on the northwest shore of Lake Shikotsu in Hokkaido's Shikotsu-Toya National Park.
Mount Eniwadake (1,320 meters in elevation) rises behind the area, and the hot spring is thought to have originated from volcanic activity in ancient times.
The spring quality is "Sodium, Calcium - Chloride / Hydrogen carbonate / Sulfate springs".
The total dissolved substances (excluding gaseous) is 1,726 mg/kg and neutral at pH 6.3.
The main source wells are 3 private sources, and the men's and women's large public baths use the source of the No. 1 well.
The large panoramic open-air bath contains a few No. 1 wells, but the No. 2 well is the main one.
The private open-air bath also draws its source from the No. 2 well.
The color of the water is clear and colorless at the time of gush, but changes to pale brown (slightly cloudy yellow) when it comes into contact with the air on the ground surface.
The inn's famous "Natural open-air bath" also has the same spring quality as the No. 1 and No. 2 wells, but strangely enough, it remains clear and colorless even after a lapse of time.

Here, we will explain the hot spring at the No. 1 well, which is the main source.
The spring source is shallow, and the water is power pumped from about 10 meters underground.
First of all, the most notable dissolved substances in the hot spring are sodium ions, which are the most abundant cation, and chloride ions, which are the most abundant anion. These are combined to form a "Sodium - Chloride spring. In the old name of the spring, it was called a "Salt spring".
Its characteristic is that it has a heat-retaining effect that warms the body to the core. The salinity of the spring prevents the sweat glands, delaying the release of heat, thus making it difficult for the water to cool down, and it is called as a "Hot springs for warmth". Chloride springs are also called "Hot springs for cuts" because of the bactericidal effect of their salinity.
Also chloride springs have a high moisturizing effect because of the coating action of the salt pack.
The indications for chloride springs are Cuts, Peripheral circulatory disturbance, Sensitivity to cold, Depression, and Dry skin.

The second most abundant anion is hydrogen carbonate ion. This ion has the effect of stimulating blood circulation in the body.
When it is combined with calcium and magnesium cations, it becomes a "Calcium (magnesium)-Hydrogen carbonate springs" or, in the old name, a "Bicarbonate earth Springs".
By the way, the new name of the spring quality of hydrogen carbonate spring was divided into 2 types of springs under the old name of "Bicarbonate earth springs" and "Sodium bicarbonate springs".
Calcium (magnesium)-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 are also called as "Hot springs for refreshing (with cooling effect)" because they promote active evaporation of moisture from the skin after bathing. Hot springs are appreciated mainly during the cold season, but this type of springs can provide a refreshing sensation after bathing even during the hot summer season.
The indications of this hydrogen carbonate springs are Cuts, Peripheral circulatory disturbance, Sensitivity to cold, and Dry skin.

The third most abundant component, the anionic sulfate ion, combines with the cationic calcium ion to form a "Calcium-sulfate spring". It is classified as a "Gypsum spring" under its old name, but the sulfate ions have healing effects on wounds and also stimulate skin elasticity, helping prevent wrinkles. For this reason, it is also called "Hot springs for cuts" and an "「Hot springs for anti-aging". Calcium ions have the effect of promoting the formation of stratum corneum, so "Calcium-sulfate springs" (under its old name: Gypsum springs) are also known as "Hot springs for beautiful skin".
The indications for sulfate springs are the same as for chloride springs, including Cuts, Peripheral circulatory disturbance, Sensitivity to cold, and Dry skin.

Currently in Japan, hot springs are classified into 10 types, but Marukoma Onsen is a blend of 3 of these types: Chloride, Hydrogen carbonate, and Sulfate springs, which makes it a superb hot spring. Moreover, the spring is neither water added, nor is it circulated and filtered, so you can experience it as a genuine "100% free-flowing hot spring water".
In the above explanation, we introduced the combination of sodium ions with chloride ions, but we would like to focus on the combination with hydrogen carbonate ions as well. This is because Sodium hydrogen carbonate (Sodium bicarbonate) is a qualifying component of hot springs.
According to the "Guidelines to the Mineral Spring Analysis Methods", the method for calculating whether the qualifying component content is present involves checking the equivalent values (mval/kg) of sodium ions and hydrogen carbonate ions, and multiplying the lesser of the two by the molecular weight of sodium hydrogen carbonate (84.01).
That is, the Hot Spring Analysis Report shows that multiplying the lesser hydrogen carbonate ion of 6.25 mval by 84.01 yields 525 mg/kg, which exceeds the standard value of 340 mg that qualifies it as a "Hot spring".
This indicates that despite the fact that Marukoma Onsen is neutral with a hydrogen ion concentration of pH 6.3, this component is responsible for the smooth, silky feeling after bathing, as if the water were alkaline (pH 8.5 or higher).

In addition, we would like to focus on undissociated components besides the above-mentioned cations and anions.
Metasilicic acid, which is said to be a natural moisturizing ingredient, amounts to 226.5 mg/kg, more than 4.5 times the standard value (50 mg/kg or more) for qualifying as a "hot spring".
There is also 34.4 mg/kg of Metaboric acid, which has a cleansing effect that prevents acne, etc., which is about 7 times the standard value (5 mg/kg or more) for qualifying as a "hot spring".
Although they are sub-elements, the presence of these two components can be considered "Hot springs for beautiful skin".
It also contains 0.8 mg/kg of Meta-arsenic acid, although this is only slightly less than the qualification standard for "hot springs" (1 mg/kg or more).
Although Meta-arsenic acid is a trace substance with toxic properties, it is believed to be beneficial for alleviating skin problems due to its anti-inflammatory effects for chronic skin diseases and atopic dermatitis, as well as its bactericidal effects.

The dissolved gas components are also noteworthy.
Because it contains 187.1 mg/kg of free carbon dioxide.
If it contains 250 mg/kg or more, it qualifies as a "hot spring", and if it contains 1,000 mg/kg or more, it can be called a "Carbon dioxide spring" which promotes blood circulation through its vasodilating effect. By the way, popular carbon dioxide bath salts contain 40 to 100 mg/kg of carbon dioxide, but this hot spring contains several times that amount. However, because of the high temperature of the spring, bubbles cannot be confirmed.

Back to the cations, it is thought that the Iron (II) Ions, which are contained at 2.7 mg/kg, are the cause of the color of the hot water, which is a characteristic of this hot spring.
If it is 10 mg/kg or more, it qualifies as a "hot spring", and if it is 20 mg/kg or more, it can be called an "Iron-containing springs".
It warms the body well and is said to be good for anemia, menopausal disorders, and menstrual disorders, and is expected to have a positive effect on women.
When this component comes to the surface and oxidizes, it changes from clear and colorless to pale brown (slightly cloudy yellow).

The reason why the color of the water in the "natural open-air bath" (formerly called "natural outdoor hot spring") mentioned above remains clear and colorless despite the same name of spring quality is because the hot spring analysis report shows that it does not contain any Iron (II) Ions.
This "natural open-air bath" is a very rare "foot gush spring" with the source of the spring located under the bathtub, and the amount of hot water changes with the seasons. It is truly a natural open-air bath.
The water level of the hot spring rises and falls according to the water level of Lake Shikotsu. The water level is deepest in summer and fall, when the rainfall increases, and shallowest in winter and early spring. In other words, the water level of Lake Shikotsu seems to affect the volume of the hot spring water.
Incidentally, of the 3 source wells, the distance between the No.1 and No.2 wells is 20 m.
The distance between the No. 1 and No.2 wells and the natural hot spring is 70 to 50 m.
The difference in color between the No.1 and No.2 wells and the natural hot spring at such a short distance is a typical example of how the character of a hot spring is determined by the filter of bedrock that the source lies underground before it comes out to the surface.

The indications for drinking by spring quality include Atrophic gastritis and Constipation in the Chloride springs.
In Hydrogen carbonate springs, Gastroduodenal ulcers, Reflux esophagitis, Impaired glucose tolerance (diabetes), and Hyperuricemia (gout).
In Sulfate springs, Biliary dysfunction, Hypercholesterolemia, Constipation...etc.
Drinking is permitted only in the No. 2 well, and can be enjoyed in the Large panoramic open-air baths of the men's and women's baths.
However, since it contains Meta-arsenic acid, it is probably safe for adults to drink a maximum of 100ml a day.

The explanation of Marukoma Onsen as described above was given mainly from the perspective of its chemical effects.
However, this is not the only effect that the hot springs have on people.
As you soak in the open-air bath of the excellent quality of the spring, look around and you will see Lake Shikotsu in its natural beauty, with the majestic Mount Fuppushidake (1,103 meters above sea level) standing just beyond it.
Surrounded by the cool, clear air of Hokkaido, the hot spring baths are sure to help heal one of the most common problems of modern people, the mental health.
The warmth of the hot spring water and the quiet environment will help to activate the parasympathetic nervous system and promote stress reduction and mental relaxation. (J)

Lake Shikotsu , surrounded by virgin forest in Shikotsu-Toya National Park, is a caldera lake overlooking Mount Tarumaesan and Mount Fuppushidake to the southeast and Mount Eniwadake to the northwest.
The lake is said to have been formed by an eruption about 40,000 years ago. It was circular in shape when it was formed, but volcanic activities enlarged Mount Eniwadake and Mount Fuppushidake, giving the lake its current constricted shape.
Some people may imagine that lakes in cooler areas like Hokkaido freeze in winter, but Lake Shikotsu is known as Japan's northernmost ice-free lake, which rarely freezes even in the middle of winter.
The reason for this is its depth, which is the second deepest in Japan after Lake Tazawa in Akita Prefecture.
With a maximum depth of 360 m and an average depth of 265 m, the lake is consistently deep throughout. Warm water is stored in its depths, preventing the water temperature from dropping completely, even in midwinter.

Lake Shikotsu is also famous for its transparency, and has been repeatedly ranked number one in Japan in the Ministry of the Environment's lake water quality survey.
The transparency of the lake is also enjoyed by tourists, who can take underwater sightseeing boats departing from the Shikotsu Lake hot spring area, where they can clearly see sockeye salmon (Himemasu) swimming beneath the surface through the boat's windows.

Lake Shikotsu is closely related to Marukoma Onsen Ryokan, and it can be said that Marukoma Onsen Ryokan exists together with Lake Shikotsu in terms of both physically and spiritually.
This inn is located on the northern shore of Lake Shikotsu at the foot of Mount Eniwadake.
The inn was founded in 1915.
Hatsutaro Sasaki, the "first generation" of the ryokan, opened the ryokan in 1915, and in 2015, it celebrated its 100th anniversary as one of the oldest ryokans in Hokkaido.
Around 1915, the world was in the midst of the World War I.
At this time, the Japan government needed to develop Hokkaido in order to acquire more resources and prepare for invasions from the north.
Therefore, the policy of increasing the number of immigrants from Honshu was adopted, and Hokkaido was actually being developed at a rapid pace.
Many of the immigrants came from the Tohoku and Hokuriku regions, but others came from all over the country, bringing a diverse range of cultures to Hokkaido.
Hatsutaro Sasaki, the founder of Marukoma Onsen Ryokan, was from Fukushima Prefecture in Tohoku and was one of the pioneers involved in the construction of a power plant in Hokkaido.

The founding of the ryokan began when the first-generation owner healed his own illness through therapeutic bathing in this untouched area.
Suffering from neuralgia, he heard a story about white smoke at the foot of Mount Eniwadake and convinced it must be a hot spring, so he went to investigate.
At that time, Lake Shikotsu was literally an "undeveloped area" with few roads and rumors of large sea snakes.
Undeterred by such fears, he went through the virgin forest and found the source of the natural open-air bath connected to Lake Shikotsu, which is still the symbol of the inn today.

It began as a thatched hut, and the cheerful personality of the first generation attracted many people, including fishermen, mountain climbers, and hot-spring cure customers.
Gradually, he expanded the facilities, slowly shaping the place into a ryokan.
At that time, there was no roads leading to the inn, so the guests had to be transported by boat.
Today, with the well-developed infrastructure, the inn is conveniently located less than an hour from New Chitose Airport, but back then, it must have been a hardship just to get there.
Even so, many visitors still come to this hot spring because it worth the journey, despite the hardships.

As the inn grew, it was passed on to Yoshie Sasaki, the famous landlady who laid the basis for a prosperous ryokan with many fans, and continued with Kinjiro, the third generation, and Yoshiro, the fourth generation.
The story of the inn's history is clearly explained on a display panel next to the front desk, which was created to celebrate the 100th anniversary of the inn's founding.
Of course, the history has not been inherited in form alone.
The hot spring source of the inn, which was found by the first generation, now has a solid stone wall dividing it from the lake, but when it was discovered, of course, it was not neatly divided.
He must have carefully searched for the source relying only on the steam rising to the surface of the lake, touching the surface of the lake and sometimes diving down to check it out for himself.
It would be easy to understand if the hot water was gushing out on land, but if the source was in a lake, one can easily imagine that it would have been extremely difficult to find it.
It's also easy to imagine the immense joy he must have felt upon discovering it.
As a hot spring enthusiast, I am honestly happy to see that such hot springs from those days remain without much change in form.

Because the water level changes along with Lake Shikotsu, it must be much more difficult to adjust the temperature of the water compared to a typical hot spring with free-flowing hot spring water.
I wonder how much easier it would be to completely separate the hot spring from Lake Shikotsu and pump up the water.
But this inn does not do so.
Keeping the source of the hot spring found by the first generation as it is, the inn always tries to provide the best hot spring, which really makes me bow down to them.
Even looking only at this, we can confirm that the wishes of the first generation have definitely been passed on.
It is an ryokan that we hope will remain in this natural setting for as long as possible, and that we will cherish it like a precious gem.

Since 2021, Mr. Kazuo Hiuke has been managing the inn as its president.
He worked for 2 years at a certified public accountants' office. After that, he attended a hotel professional training school and joined a major hotel chain, where he learned the basics of management. In 2007, he joined a major resort hotel group, where he served as a leader, revitalizing and opening numerous ryokan and hotels. He then took over Marukoma Onsen Ryokan.
Although he is a professional manager, his roots lie in the second son of a long-established ryokan in Kinosaki Onsen, Hyogo Prefecture.
In a short period of time, he has increased the level of customer satisfaction and, of course, the business performance of the ryokan, while making the best use of the traditional qualities of onsen ryokans.
His efforts day and night to keep this hot spring ryokan, with its natural surroundings and unique story, going strong for many years to come is a remarkable achievement.

Marukoma Onsen Ryokan, while being a secluded hot spring inn with only one lodging, offers a stay that feels like a resort hotel harmoniously integrated with the surrounding wilderness. Its unparalleled character is undeniably filled with a charm that surpasses that of other hot spring ryokans.