A vast 3,000-tsubo Japanese garden, an onsen property showcasing the architectural beauty of a famous architect and cultural heritage.

Sanyo-so, nestled in the embrace of Genjiyama in Izu Nagaoka. Enjoy a leisurely stroll through the 3,000-tsubo garden that beautifully reflects the changing seasons, relax in the large public bath, or indulge in a private soak with Onsen water flowing directly into your room. The main building showcases the grandeur of traditional Japanese architecture, while the new wing features exquisite sukiya-style design by renowned architect Togo Murano.

  • Even before our visit, you kindly and attentively accommodated our requests, such as providing a floor chair and securing parking.Not only were the Room and each Facility wonderful, but the hospitality of the staff was also outstanding. Despite it being during the summer vacation season, we were able to spend a calm and relaxing time far from the crowds, and even my usually picky wife kept saying, “I want to come back here again.”Thank you very much.

    mercury 1984 8/11/2026
  • We stayed here with our pet.We visit every year, and we look forward to the updates each time.The meals have returned to a heavier style, and we are very satisfied with both the quality and quantity.This is our favorite Accommodation for both the Room Facility and the service.We will definitely stay again.

    まぶさだ 7/6/2026

Facilities and Services

See All
  • Hot spring
  • Spa facility
Open-air bath / Large public bath / Free shuttle service
IN15:00~17:00
OUT11:00
Number of rooms22 rooms
PetNot allowed
Your childPermitted

Accommodation Plan with Moon Terrace Lounge Admission Ticket Included

IN 15:00~18:00
OUT 11:00
¥102,000
Dinner and Breakfast included ; 2 peopleTax included¥76,500
(USD 479.50)

"Early Bird 60" Plan: Enjoy a Discounted Stay with Early Reservation (Dining Area / Matsu Course)

IN 15:00~18:00
OUT 11:00
¥103,134
Dinner and Breakfast included ; 2 peopleTax included¥77,359
(USD 484.88)

Accommodation Plan with Moon Terrace Lounge Admission Ticket Included

IN 15:00~18:00
OUT 11:00
¥110,600
Dinner and Breakfast included ; 2 peopleTax included¥82,950
(USD 519.93)

"Early Bird 60" Plan: Enjoy a Discounted Stay with Early Reservation (Dining Area / Matsu Course)

IN 15:00~18:00
OUT 11:00
¥120,434
Dinner and Breakfast included ; 2 peopleTax included¥90,334
(USD 566.21)

Accommodation Plan with Moon Terrace Lounge Admission Ticket Included

IN 15:00~18:00
OUT 11:00
¥110,600
Dinner and Breakfast included ; 2 peopleTax included¥82,950
(USD 519.93)

"Early Bird 60" Plan: Enjoy a Discounted Stay with Early Reservation (Dining Area / Matsu Course)

IN 15:00~18:00
OUT 11:00
¥120,434
Dinner and Breakfast included ; 2 peopleTax included¥90,334
(USD 566.21)

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Onsen Accommodation With No Meals Included

Introduction of the Accommodation

Exterior
Exterior
Interior
Guest Rooms
Onsen
Exterior
Exterior
Experience the charm and elegance of nature at a historic Onsen accommodation, designated as a tangible cultural property.

Sanyo-so, nestled in the embrace of Mount Genjiyama in Izu Nagaoka, is a prestigious and elegant accommodation. Originally built as a villa for Hisaya Iwasaki, the eldest son of Yataro Iwasaki, founder of the former Mitsubishi conglomerate, this luxurious property features traditional Japanese Sukiya-style architecture within a grand Japanese garden. Designed by Kyoto gardener Jihei Ogawa, the 3,000-tsubo (approximately 9.9 acres) garden is surrounded by rich nature and offers an extraordinary experience unique to an Onsen retreat with seasonal beauty and tranquility. Enjoy a blissful stay reminiscent of an imperial villa.

Guest Rooms
Guest Rooms
Guest Rooms
Guest Rooms
Guest Rooms
Rooms
Guest Rooms
Guest Rooms
Guest Rooms
Guest Rooms
Guest Rooms
Guest rooms consisting of the New Wing and Main Building

The new building features pure Japanese-style Sukiya architecture designed by the renowned architect Togo Murano, a recipient of the Order of Culture. Each Room is arranged with a small private garden, allowing you to enjoy your own personal space. These are masterpieces crafted with exceptional skill by artisans of the Heisei era. The names of the Rooms are inspired by "The Tale of Genji." The main building, cherished for its historical significance, has long been loved by distinguished guests as a precious example representing Japanese Ryokan architecture. It was created through the craftsmanship and competition among master artisans. Within the Japanese garden lies "Hanare," a detached Room offering tranquility, and on an elevated location is the "Japanese Suite," providing sweeping views of the garden. The names of these Rooms are derived from traditional Noh theater themes.

Cuisine
Cuisine
Cuisine
Cuisine
Cuisine
Cuisine
Cuisine
Exquisite craftsmanship by master artisans of traditional Japanese art

Izu Nagaoka is rich in both seafood and mountain delicacies. The charm of the meals at Sanyo-so lies in their exquisite presentation. Each dish, crafted with seasonal ingredients and meticulous care, will satisfy both your appetite and your heart.

Onsen
Indulge in a luxurious time enjoying the free-flowing Onsen to your heart's content.

The high-concentration alkaline Onsen with a pH of 9.1 offers soft, odorless, and tasteless water that gently nourishes the skin. Known for its effectiveness in relieving nerve pain, muscle pain, and cold sensitivity, as well as its high skincare benefits, Izu Nagaoka Onsen provides a blissful retreat. All rooms feature private flowing Onsen baths, allowing you to enjoy a relaxing soak at your convenience and indulge in the ultimate bathing experience.

Exterior
Spacious Grounds

Detached-style guest rooms within a vast 42,000-tsubo property. A stunning 3,000-tsubo Japanese garden showcasing the beauty of seasonal transitions. Enjoy an exquisite time surrounded by flowers and plants that change with the seasons.

Exterior
Registered Tangible Cultural Property

The main building of Sanyo-so was constructed in 1929 as a refined sukiya-style Japanese residence for Hisaya Iwasaki, the eldest son of Yataro Iwasaki, the founder of the former Mitsubishi conglomerate. It is set within a magnificent Japanese garden designed by Kyoto landscape architect Jihei Ogawa. In June 2017, it was registered as a Tangible Cultural Property by the Agency for Cultural Affairs, recognizing its value as a national treasure.

Exterior
Local Attractions

A direct route to the summit of Mount Katsuragi at an elevation of 452 meters. Enjoy a scenic aerial journey on the approximately 3,600-meter round-trip ropeway at Izu Panorama Park, offering breathtaking views. Additionally, visit the Mishima Skywalk Suspension Bridge, where you can take in panoramic vistas of Mount Fuji, Suruga Bay, and the mountain ranges of Izu from above.

Facilities and Equipment of Accommodation

  • The room
    The room
  • Hot Springs & Baths
    Hot Springs & Baths
  • Facilities & Services
    Facilities & Services
  • Meal
    Meal

Notice from the Accommodation

  • Moon Viewing Deck

    Moon Terrace Lounge

    [Moon Terrace Lounge – An Evening on the Moon-Viewing Terrace -]
    To celebrate the Mid-Autumn Harvest Moon, we will host an autumn-only lounge event on the Moon-Viewing Terrace.
    Savor a relaxing evening with drinks and live music.

    [Dates] Friday, September 25 – Sunday, September 27, 2026
    *Each day features a different program and atmosphere.

    [Time] 5:30 P.M. – 8:30 P.M. (scheduled)

    [Venue] Izu Nagaoka Onsen Sanyo-so, Moon-Viewing Terrace
    *In case of rain, the event will be held indoors.

    [Performers]
    • Fri, Sep 25: Flute Saki Tanaka / Keyboard Ikuyo Minagawa
    Enjoy elegant live performances by flute and keyboard. Their gentle tones beautifully complement the moonlit night.

    • Sat, Sep 26: Izu Nagaoka Performing Arts Cooperative Association
    Experience traditional Japanese culture with dances performed by geisha entertainers, bringing you a charming autumn evening.

    • Sun, Sep 27: Violin Naomi Tarui / Guitar Yuki Sasaki
    Live jazz by violin and guitar. Enjoy a refined moment for adults with sophisticated melodies.

    [Schedule]
    From 5:30 P.M.: Dinner at the dining venue
    ● Moon Terrace Lounge opens
    From 7:30 P.M.: Daily jazz performance / geisha dance performance
    From 8:30 P.M.: Moon Terrace Lounge closes

  • Summer Menu Introduction: June 16–September 15 (tentative)

    From Tuesday, June 16, 2026 to Tuesday, September 15, 2026, we will offer our summer menu.

    Seasonal appetizers include a cream cheese tofu styled to resemble ice, and Umibudo (sea grapes) from Numazu.
    Our salt-grilled ayu (sweetfish) is served with tade vinegar—made by grinding tade leaves and thinning them with rice starch water and vinegar. Please enjoy this traditional summer condiment that pairs perfectly with ayu.
    For simmered dishes, we offer a refreshing chilled selection. Each vegetable is simmered in a different dashi broth and served with a dashi jelly that seals in the umami for a cool, elegant finish.

    Savor the flavors of summer brought to you by the season.
    *Menu items may change depending on the season and ingredient availability.

  • Relaxation Salon Gara

    Recommended Courses at the Relaxation Salon “GARA”

    We are pleased to introduce recommended courses at the relaxation salon “GARA -GARA-”.
    Enjoy a soothing moment with our all-hand treatments.

    ●Body Therapy Course
    60 min: 16,500 yen
    75 min: 19,800 yen
    90 min: 23,100 yen
    While relaxing with the aroma fragrance, we provide massages for the back, legs, and scalp.
    Improved lymphatic flow can help relieve fatigue and support detoxification.

    ●Brightening & Lift-Up Facial and Decollete Course
    60 min: 16,500 yen
    A lift-up course featuring facial and decollete care plus a head massage.

    Hours / 3:00 P.M. – 10:00 P.M.
    Location / Sanyo-so Annex (Shinkan), 2nd floor (before the large public bath)

    *Closed on Tuesdays and Wednesdays.
    *Reservation required. Same-day Reservation accepted until 6:00 P.M. (*Last treatment start time: 9:00 P.M.)

Basic Information

TaxesHot Spring Tax
Card information
VISA / MASTER / JCB / AMEX / DINERS / UnionPay
Pets
Not allowed
BreakfastThere is no information about breakfast.
Your child
You can stay.
There is no child rate setting. Please include children of elementary school age or older in the number of paid accommodation guests when making a reservation.
Room service
Not available
Common amenities
  • ○ Shampoo · conditioner
  • ○ Body soap · soap
  • ○ Towel · Bath towel
  • × Body towel · sponge
  • ○ Toothbrush set
  • ○ Comb · Brush
  • ○ Shower cap
  • ○ Hair dryer
  • ○ Shaving
  • × Shaving Gel/Foam
  • × Bath additives
  • ○ Yukata
  • × Nightwear
  • × Bathrobe
  • × Slippers
  • ○ facial cleanser
  • ○ Toner
  • ○ Lotion
  • ○ Makeup remover
  • ○ Cotton swab
  • × Cotton
  • ○ Clothing deodorizing spray
  • ○ Refrigerator
  • × Minibar
  • ○ Electric kettle
  • ○ Tea set (free)
  • ○ Television
  • ○ Safe
  • × Scale
  • × Trouser press
  • × Free morning edition
  • × Pay-per-view broadcast
  • ○ Satellite broadcasting
  • × Video on Demand
  • × Radio
  • × CD player
  • × DVD player
  • × Blu-ray player
  • × Speakers for portable audio
  • × In-room PCs and tablets
Facilities and Features
  • ○ Hot spring
  • × Rooms with open-air baths available
  • ○ Open-air bath
  • × Free-flowing hot spring
  • ○ Large public bath
  • × Private bath
  • × Sauna
  • × Ganbanyoku (rock bathing)
  • × Within a 5-minute walk from the station
  • × Within a 5-minute walk to the convenience store.
  • × Indoor pool
  • × Outdoor pool
  • × Pet-friendly
  • ○ Spa facility
  • × Fitness
  • ○ Free shuttle service
  • × Shuttle Service (Paid)
  • × Room service
  • × Room Service Available 24 Hours
  • × Barrier-free
  • × Childcare services
Esthetic Massage
Available
Facial Course (40 minutes) ¥9,900 Facial & Décolleté Course (60 minutes) ¥13,200 Hand Treatment Course (20 minutes) ¥3,300 Back Treatment Course (30 minutes) ¥7,700 Scalp Treatment Course (30 minutes) ¥7,700 Relaxation Course (120 minutes) ¥25,300 Short Relaxation Course (90 minutes) ¥19,800
Fitness gym
None
Public Bath
The number of Public Bath
2
Business Hours
15:00~10:00
Hot spring
Available
Free-flowing
None
Milky hot spring water
None
Additional Information
Remarks
Business hours: 3:00 P.M. - 9:30 A.M.
Open-air bath
The number of Open-air bath
2
Business Hours
---
Hot spring
Available
Free-flowing
None
Milky hot spring water
None
Additional Information
Remarks
Available hours: 3:00 P.M. ~ 12:00 MID. / 6:00 A.M. ~ 9:30 A.M.
Spring quality and benefits

Alkaline Simple Onsen

Rheumatic diseases, musculoskeletal disorders, nerve paralysis, post-illness recovery period

SaunaNone
Hot stone spaNone

Reviews

Overall Score
4.46
Good (45)
  • Rooms & Amenities
    4.38
  • Facility
    4.53
  • Hospitality & Service
    4.47
  • Meals
    4.24
  • Onsen & Bath
    4.64
  • Satisfaction
    4.51

*Reviews that have been translated from Japanese.*

*Showing only reviews from 一休.com (Japanese) and Yahoo!トラベル.*

Access Information

Address
Shizuoka Prefecture270 Mamanoue, Izu no Kuni City
TEL:+81-55-947-1111

■If arriving by car
Approximately 26km via the Izu-Jukan Expressway and Izu-Chuo Road (Nagaoka-Kita I.C.) from the Tomei Expressway Numazu I.C. / Shin-Tomei Expressway Nagasawa-Numazu I.C.

■If using the train
Transfer to the Izuhakone Railway at Mishima Station on the Tokaido Shinkansen for about 20 minutes, then take a taxi from Izu-Nagaoka Station for approximately 5 minutes under normal conditions (about 810 yen).
A complimentary shuttle bus exclusively for guests operates from Izu-Nagaoka Station. (Reservation required)
The direct limited express "Odoriko" departing daily from Tokyo Station and every Saturday from Shinjuku Station is also convenient.

Parking Information
Fee
Free for guests
Parking time
---
Parking space
No restrictions
Number of parking spaces
20 cars available outdoor
Valet service
Unavailable
Capable of parking 3 large buses

Pickup and drop-off information
Available (Free)From Izu-Nagaoka Station to Sanyo-so
14:00
14:30
15:00
15:30
16:00
16:30
17:00

From Sanyo-so to Izu-Nagaoka Station
10:00
10:30
11:00
11:30

■ The shuttle service is by Reservation only. Please make a reservation in advance. (Tel: 055-947-1111)
■ Reservations will close once the capacity is reached.
■ Please note that due to road conditions or Reservation status, the service may not operate as scheduled or may be suspended.

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