Overview

Sanyo-so brings you to Izu Nagaoka Onsen, at the foot of Mt. Genji, with a history that reaches back to 1929. The main building was first built as the villa of Hisaya Iwasaki, the eldest son of Yataro Iwasaki, founder of the former Mitsubishi conglomerate. Today, it remains one of Izu’s most graceful ryokan stays, with registered cultural property architecture, sukiya-style rooms, and a large Japanese garden designed by Kyoto garden master Jihei Ogawa.

This is a ryokan for you if you want space, history, and real hot spring comfort. You can walk through the 3,000-tsubo garden, soak in free-flowing Izu Nagaoka Onsen water in your room, enjoy seasonal kaiseki at Yuho, and spend time in buildings shaped by leading Japanese architects and craftsmen. The atmosphere feels dignified and quiet, without losing the warmth of a traditional ryokan stay.

Accommodation

Sanyo-so offers Japanese-style and Japanese-Western rooms across the Main Building and New Building. The Main Building carries the strongest historical atmosphere, with rooms connected to traditional Noh names and details such as alcove posts, transoms, beams, and wooden fittings that differ from room to room. The New Building was designed by architect Togo Murano and follows traditional sukiya-style architecture, with rooms arranged around small private gardens and names inspired by “The Tale of Genji.”

Every room includes free-flowing hot spring water, so you can enjoy Izu Nagaoka Onsen in your own room at any time during your stay. The room baths differ in size and style, but the private hot spring experience is part of every stay at Sanyo-so.

The most spacious rooms include multi-room suites with separate sleeping, sitting, and living areas. Some rooms offer a stronger traditional feel with tatami and futon bedding, while others combine tatami rooms with Western-style beds. The Japanese-Western rooms work well when you want the atmosphere of a ryokan but prefer bed-style sleeping. Selected rooms also include garden-facing layouts, wide verandas, or private inner gardens.

Sanyo-so also has a dog-friendly detached room, Fujinouraba, designed for stays with small dogs. This room includes its own garden and hot spring bath, with dog-friendly items such as a bathtub, foot-washing area, cage, toilet tray, towels, and other useful supplies prepared for your stay.

Dining

Dining at Sanyo-so centers on seasonal Japanese kaiseki at Yuho. Izu offers both seafood and mountain ingredients, and the kitchen uses local produce and selected ingredients to create dishes that reflect the time of year. Each course is prepared with attention to color, balance, texture, and presentation, so the meal feels connected to the garden, the architecture, and the rhythm of the season.

Dinner may include seafood from the Izu area, mountain vegetables, seasonal soups, grilled dishes, simmered dishes, rice, and dessert. The course changes with the season and plan, so the food feels fresh to the moment of your stay rather than fixed throughout the year.

Yuho also has a cultural detail worth noticing: the stage wall displays “Hoko,” a kirikane work by Sayoko Eri, a Living National Treasure. This gives the dining room a stronger sense of craft and Japanese artistry.

A Buddhist vegetarian shojin ryori menu can be arranged with advance reservation. This option must be requested several days before arrival, making it useful if you want a plant-based Japanese meal prepared with care.

Onsen and Wellness

Sanyo-so uses Izu Nagaoka Onsen, a hot spring with a soft, smooth feel on the skin. The water is an alkaline simple spring with a pH of 9.1. It has a gentle texture, no strong smell, and is known for warming the body while leaving the skin feeling comfortable.

The large public bath area includes indoor and open-air baths. The indoor bath is available from the afternoon until the following morning, while the open-air bath has separate evening and morning hours. You can enjoy the shared baths when you want a larger bathing space, then return to your room for private hot spring bathing whenever you like.

Every room also includes free-flowing hot spring water. This gives you the best part of the ryokan’s onsen experience in your own room, without needing to follow the public bath schedule. The hot spring water is associated with support for rheumatic concerns, movement-related discomfort, nerve-related concerns, and recovery after illness.

Relaxation salon GARA offers all-hand treatments designed to ease tension in the nerves and muscles while supporting circulation. Body therapy, facial care, hand care, back care, scalp care, and nail care are available by reservation, giving you another way to add rest to your stay after bathing.

Guests with Tattoos

Sanyo-so has shared public indoor and open-air hot spring baths. Tattoos are not permitted in the shared bathing areas. Every room includes a private free-flowing hot spring bath, so you can use the bath in your own room instead.

Facilities

Sanyo-so has a 3,000-tsubo Japanese garden, Main Building cultural property spaces, New Building sukiya-style architecture by Togo Murano, public indoor and open-air hot spring baths, private in-room hot spring baths, the restaurant Yuho, Bar Kanogawa, Lounge Aoi, a souvenir shop, Tsukimi-dai moon-viewing platform, relaxation salon GARA, parking, and accessibility support such as wheelchair rental and slopes in selected areas.

The garden is one of the strongest parts of the stay. Designed by Jihei Ogawa, it includes a central pond, garden paths, seasonal flowers, and a hilltop pavilion where you can look over the grounds and toward the mountains behind the ryokan. Spring brings cherry blossoms, dodan-tsutsuji, and satsuki; summer brings iris and water-side greenery; autumn brings red maples; winter brings plum blossoms and cold-season flowers.

Lounge Aoi sits in a round building designed by Togo Murano. You can stop here for freshly brewed coffee, tea, soft drinks, beer, and a quiet view of the ryokan’s design details. The souvenir shop inside the lounge area carries local items, and you can browse even without ordering a drink.

Bar Kanogawa is located behind Yuho and opens on selected days before holidays. It gives you a calm after-dinner space for drinks. Tsukimi-dai, the moon-viewing platform, was restored in May 2026 and is used as a cultural space for enjoying the Japanese tradition of moon viewing.

Activities

Sanyo-so gives you several ways to experience Izu Nagaoka without rushing. You can walk through the garden, visit the hilltop pavilion, spend time at Lounge Aoi, enjoy the public baths, book a treatment at GARA, or stay mostly in your room and use your private hot spring bath.

Cultural plans and events may include geisha entertainment, goshuin temple and shrine visits around Izunokuni, jazz events at Tsukimi-dai, seasonal garden café experiences, and architecture-focused programs connected to Togo Murano’s design. These experiences change by season and availability.

Nearby, you can visit Izu Panorama Park for the ropeway to Mt. Katsuragi, where clear days bring views toward Mt. Fuji, Suruga Bay, and the Izu landscape. Mishima Skywalk, Numazu Port’s Byuo observation water gate, and Shuzenji Niji-no-Sato also make good outings when you want to add more sightseeing to your ryokan stay.

Additional Features

Sanyo-so is best for you if you want a historic Izu ryokan with a 3,000-tsubo Japanese garden, registered cultural property architecture, sukiya-style rooms, free-flowing hot spring water in every room, shared indoor and open-air baths, seasonal kaiseki dining, a bar, a lounge, and access to cultural experiences around Izu Nagaoka.

Check-in starts at 15:00, and check-out is at 11:00. You also have parking, shuttle service from Izu-Nagaoka Station by advance reservation, all-room free-flowing hot spring bathing, selected dog-friendly accommodation, relaxation treatments, a souvenir shop, Lounge Aoi, Bar Kanogawa, and access to nearby attractions such as Izu Panorama Park, Mishima Skywalk, Numazu Port, and Shuzenji Niji-no-Sato.