Kyushu > Oita > Yufuin Onsen
100% Natural free-flowing silky hot spring
Yufu-no-Oyado HOTARU
由布のお宿 ほたる
1791-1 Kawakita, Yufuin-cho, Yufu, Oita 879-5114, JAPAN
Phone：+81-(0)977-84-5151
Spring Quality
Alkaline Simple Hot Springs
アルカリ性単純温泉
(Hypotonic, Alkaline, High temperature spring)
Yufuin's Highest pH 9.7／
Velvety Hot Spring for Beautiful Skin／
100% Free-Flowing Onsen for Deep Relaxation
Hot springs are believed to form when rainwater or snowmelt seeps underground, or when ancient seawater becomes trapped deep within the earth. Heated by magma or the earthʼs internal heat, this water dissolves minerals from underground rocks and slowly rises to the surface over years—or even tens of thousands of years.
Onsen Components
* % values are simplified representations of mval%.
52.10 mg/kg
■ Enhances the skin's moisture retention and helps prevent dryness
■ Promotes blood circulation and helps relieve sensitivity to cold
■ Relieves muscle tension
28.70 mg/kg
■ Creates high alkalinity
■ Produces a velvety skin feel
■ Softens dead skin cells and enhances skin-beautifying effects
39.10 mg/kg
■ Supports skin regeneration
■ Helps promote blood circulation
■ One of the main components of “Hot springs for beautiful skin”
45.70 mg/kg
■ Cleansing action that removes sebum and impurities
■ Smooths the skin
■ One of the main components of Hot springs for beautiful skin
*The bars for Metasilicic acid 50 mg/kg and Metaboric acid 5 mg/kg represent the qualification criteria for hot springs. The number of bars indicates values such as “more than XX times the hot spring standard” or “about XX times the hot spring standard”.
■ Natural moisturizing component
■ More than 2 times
the hot spring standard (50 mg/kg)
＋
＋
Total Dissolved Substances
(excluding gaseous)
297.4 mg/kg
2～3 times more components than commercial bath additives!
Hydrogen Ion
Concentration
pH 9.7
Alkaline
Spring Temperature
43.6 ℃
The flow rate is adjusted to maintain the ideal temperature
Color of water /
Smell of water
Clear and Colorless
Odorless
Hot Spring Flow Rate
70 L/min
(Private source / Mechanically pumped)
Hot spring water usage per person (spring discharge / maximum capacity)
→ 70 L / 35 guests ＝2 L / per minute
* To meet the requirements for kakenagashi (flowing directly from the source),
at least 1 liter of hot spring water per minute per bather
is required for proper bath management
Status of Source Utilization
| Water added | Heated | Disinfected | Circulated | Bath additives |
|---|---|---|---|---|
| No | No/Yes | No | No | No |
* Partially heated only in winter
Men's Open-Air Bath
The hot spring features alkaline water with a silky, lotion-like texture that feels wonderfully smooth on the skin, making it especially popular with women. Guests can also enjoy the luxury of 100% natural free-flowing hot spring water from the property's own private source. At selected times of the day, the open-air bath is available free of charge as a private bath (excluding the day before holidays and public holidays).
Skin Feeling Gauge
Ideal for:
People who want silky smooth skin
People who prefer mild hot springs
People with sleep difficulties
People feeling stressed
People recovering from injury or illness
People seeking skin‑beautifying effects
Indications by Spring Quality
(for bathing)
Autonomic instability
Insomnia
Depression
General Indications (for bathing)
Chronic pains or stiffness of muscles or joints (chronic phase of rheumatoid arthritis, osteoarthritis, lower back pains, nerve pains, frozen shoulder, bruises, sprains, etc.), Muscle stiffness in motor paralysis, Sensitivity to cold, Peripheral circulatory disturbance, Gastrointestinal hypofunction (slow digestion, intestinal gas formation, etc.) Mild hypertension, Impaired glucose tolerance (diabetes), Mild hypercholesterolemia, Mild asthma or Emphysema, Hemorrhoidal pains, Autonomic instability, Various symptoms from stress (sleep disorders, depression, etc.), Restorative phase from illness, Recovery from fatigue, Health promotions
General Contraindications (for bathing)
Active stage of diseases (especially when fever is accompanied), Active tuberculosis, Advanced
malignant tumor or the case of significant debility involving severe anemia, Severe cardiac or lung
diseases involving suffocation feelings with a little movement, Severe kidney diseases involving
edema, Gastrointestinal bleeding, When bleeding is visible, Acute exacerbation stage of chronic
diseases
*There are no general indications or contraindications for drinking.
Onsen Power Chart
→ 100% natural free-flowing hot spring water
All baths are supplied with 100% natural free-flowing hot spring water
Skin Beauty Power Chart
Private bath (Family bath) “Tsurumi-no-Yu”
The inn offers two indoor baths that can be reserved for private use, available 24 hours a day at your convenience. Each bath, thoughtfully designed around natural rock formations, is perfectly sized for two adults. Relax in 100% natural free-flowing hot spring water while taking in the magnificent view of Mt. Yufu through the large picture window.
Keywords of this Onsen
In-Room Semi-Open-Air Hinoki Bath
Rooms 103 and 105 feature an in-room semi-open-air hinoki bath. The fragrant cypress tub, paired with large open windows, creates a wonderfully airy atmosphere. Soak in 100% natural free-flowing hot spring water while enjoying spectacular views of Mt. Yufu for a truly unforgettable bathing experience.
Onsen Classification
️Hot springs are classified not only by their spring quality, but also by three additional factors: osmotic pressure, hydrogen ion concentration (pH level), and spring temperature.
Osmotic Pressure
(Hypotonic, Alkaline, High temperature spring)
In hot spring classification, “osmotic pressure” refers to comparing the concentration of dissolved components in the spring water (mainly salts) with that of human body fluids (such as blood and intracellular fluid). Based on this comparison, springs are categorized as hypotonic, isotonic, or hypertonic. The difference in concentration serves as an indicator of how easily water moves between the hot spring water and body fluids.
Total Dissolved Substances
297.4 mg/kg
Classified as a Hypotonic spring
|
|||||
 |
Isotonic 👤 Body fluid concentration ≒ ♨ Onsen concentration Water・・・Hardly moves into or out of the body Onsen components・・・Minimally absorbed and act gently on the body Isotonic means having the same osmotic pressure as human body fluids. It is equivalent to a saline solution made by dissolving approximately 8.8 g of salt in 1 liter of water. Because its concentration is close to that of body fluids, there is little movement of water or onsen components due to osmotic pressure. As a result, it is considered to place the least strain on the body and to be the gentlest in terms of stimulation. |
||||
 |
Hypertonic 👤 Body fluid concentration ＜ ♨ Onsen concentration Water・・・Easily moves out of the body Onsen components・・・Easily absorbed into the body Because its osmotic pressure is higher than that of human body fluids (isotonic fluids), water tends to move out of the body more easily, while onsen components are more readily absorbed into the body. As a result, stronger therapeutic effects may be expected. However, hypertonic hot springs are also more likely to cause “hot spring fatigue (yu-atari)” and can be more physically demanding. They are generally regarded as “rich or highly concentrated hot springs”. Among Japanese hot springs, hypertonic springs are relatively uncommon, and a comparatively large proportion are classified as mineral springs (below 25°C) rather than hot springs (25°C or higher). |
||||
Hydrogen Ion Concentration
(Hypotonic, Alkaline, High temperature spring)
In the hot spring analysis report, the section titled “Examination and test results at gushing location” includes the listed pH value. Chemically, a pH of 7.0 is considered neutral; values below this are acidic, and values above it are alkaline. According to the “Guidelines for the Mineral Spring Analysis Methods”, the chemical nature of a mineral spring is classified based on its pH value at the time of emergence, as shown in the table below.
pH 9.7
Classified as Alkaline
Spring Temperature
(Hypotonic, Alkaline, High temperature spring)
43.6℃
Classified as High temperature spring
Under the “Hot Springs Act”, water that contains one or more designated substances at or above the legally specified levels and has a source temperature of 25°C or higher is classified as a “hot spring”. If the temperature is below 25°C, it is labeled a “mineral spring”. Furthermore, as noted above, hot springs are classified by source temperature as high-temperature spring, hot spring, or low-temperature spring.
In-Room Rock Open-Air Bath
The open-air baths in Villas 2 and 3 feature natural rock tubs that create a wonderfully rustic atmosphere. Spacious enough for two adults, they offer a relaxing soak while overlooking the magnificent Mt. Yufu, with breathtaking views from the bath.
Summary
The hot spring at “Yufu-no-Oyado HOTARU” is Alkaline Simple Hot Springs. With an ideal spring temperature of 43.6°C, the water can be enjoyed 100% natural free-flowing, making it a favorite among onsen enthusiasts. The gentle, low-irritation water helps relax both body and mind and may help relieve autonomic instability, insomnia, and depression. In addition to the freshness of its private source, the spring is notable for its exceptionally high alkalinity (pH 9.7), even among Yufuin’s hot springs, giving the water a distinctive smooth, lotion-like feel. The water also provides a gentle cleansing effect that helps remove dead skin cells, while metasilicic acid, present at more than twice the hot spring standard, acts as a natural moisturizing component to help keep the skin hydrated. Together, these qualities have earned it a reputation as “lotion-like Hot springs for beautiful skin”.
Facility Data
| Founded in | 2003 (Heisei 15) |
|---|---|
| Check in | 3:00 PM |
| Check out | 10:00 AM |
| Location | A secluded inn with panoramic views of Mt. Yufu and the surrounding countryside |
| Rooms | Total 12 rooms |
| Capacity | 35 people |
| Parking | 20 cars |
| Facilities | Dining Room, Gift Shop, Treatment Room |
| Internet | Wi-Fi available |
| Barrier-free | Supported (1 Barrier-free Western style room) |
| Bidet toilet | Equipped |
Keywords for this inn
| Free-flowing silky, lotion-like hot spring water |
| Generously sized in-room open-air bath |
| Unlimited use of complimentary private baths |
| Magnificent views of Mt. Yufu from private baths and guest rooms |
| Seasonal kaiseki dinner featuring local ingredients |
Hot Spring (Onsen) Report
| Yufuin Onsen boasts the second largest volume of hot springs in Japan, following Beppu Onsen in Oita Prefecture. Most of its springs are simple hot springs, but each of the source wells in the Yufuin basin has slightly different characteristics. Yufu-no-Oyado HOTARU 's spring water is an Alkaline Simple Hot Springs with a Hydrogen ion concentration (pH value) of 9.7, one of the highest among Yufuin's hot springs. Since human skin is generally slightly acidic, soaking in alkaline hot spring water causes the surface of the skin to react and dissolve dead skin cells. This results in a silky smooth skin texture. However, because the pH value of the hot springs here is particularly high, the texture of the hot spring water is more than smooth; it would be more accurate to describe the water as thick and creamy. The feeling of the water clinging to the skin can be felt as soon as one takes a bath. The clear, colorless water is also referred to as “Hot spring water like lotion” by regular visitors・・・ Read more → |
Transportation Access
| By train | From JR Hakata Station, approx. 2 hours on the limited express Kudaihonsen Line → 7 min. by taxi from JR Yufuin Station From JR Oita Station, approx. 50 min. on the limited express train Kudaihonsen Line → 7 min. by taxi from JR Yufuin Station From Fukuoka Airport: 1 hr. 35 min. by highway bus → 3 min. by taxi from Michi no Eki Yufuin From Oita Airport: 55 min. by highway bus → 7 min. by taxi from JR Yufuin Station |
|---|---|
| By bus | 15 min. walk / 6 min. drive from Yufuin Station Bus Center |
| Shuttle bus | Available for overnight guests. Pick-up at JR Yufuin Station and Yufuin IC (3:00 p.m. to 6:00 p.m. for pick-up, anytime for drop-off) |
| By car | Oita Expressway Yufuin IC → Turn right at the first traffic light, 2 min. |
| Address | Oita／Yufuin Onsen／Yufu-no-Oyado HOTARU 1791-1 Kawakita, Yufuin-cho, Yufu City, Oita Prefecture, 879-5114, JAPAN TEL:+81-(0)977-84-5151 |