Imabari Radium Onsen Main Hall: A Taisho-Era Architectural Treasure
Rising above the central streets of Imabari City in Ehime Prefecture, the Imabari Radium Onsen Main Hall (今治ラヂウム温泉本館) stands as one of the most extraordinary surviving examples of early 20th-century Japanese architecture. With its striking polygonal tower, twin octagonal domes, and brick chimney, this reinforced concrete bathhouse has been a beloved landmark for over a century. Registered as a national tangible cultural property in 2016, the building is a rare survivor of the devastating Imabari air raids of World War II and continues to captivate architecture enthusiasts, researchers, and visitors from around the world.
Historical Background
The story of the Imabari Radium Onsen begins with Murakami Kanzō, an enterprising businessman from Ōshima Island in the Seto Inland Sea. A descendant of the famed Murakami Suigun (Murakami pirates) and a successful timber merchant, Murakami envisioned transforming a marshy lotus root field in central Imabari into a thriving entertainment district. In 1919 (Taishō 8), he constructed the "Kyōrakukan" — a grand entertainment complex featuring a cinema, bathhouse, dance hall, and dining facilities — as the centerpiece of what would become the Kyōmachi entertainment quarter.
The area that Murakami developed was named "Kyōmachi" after his father Kyōzō's name, and it grew into a vibrant commercial and leisure district. Following a road construction project in 1926 that divided the original site, the bathhouse portion was formally named "Radium Onsen" in 1927. The concept of "radium baths" was fashionable in the Taishō era, reflecting the early 20th-century fascination with radioactive elements believed to have therapeutic properties.
During the Pacific War, the building's sturdy reinforced concrete construction led to its requisition as the headquarters of the Ochi-gun Homeland Defense Corps around 1942. When the devastating Imabari air raids of 1945 destroyed approximately 80% of the city center, the Radium Onsen miraculously survived the firestorm. In the immediate aftermath, the building's second-floor grand hall served as an emergency hub for hospitals, banks, and other essential services, playing a vital role in the city's recovery.
After the war, the second floor continued to serve as a dance hall, and in the 1960s, a third-floor addition was built to create "Hotel Seiunkaku." In 1988, the bathing facilities were modernized with saunas, jet baths, and other contemporary amenities. However, due to aging facilities and the decline of public bathhouse culture, the bathhouse ceased operations in March 2014.
Why It Was Designated a Cultural Property
On November 29, 2016, the Imabari Radium Onsen Main Hall was registered as a nationally registered tangible cultural property — the first such designation in Imabari City. The building was recognized for several outstanding characteristics.
First, it possesses an exceptionally unusual architectural form. The flat-roofed main structure is crowned at its center by a tower composed of a pentagonal plan layered with a hexagonal plan, while the rear of the building features twin octagonal domed bathrooms arranged side by side for male and female bathers. This combination of geometric forms creates an appearance unlike any other bathhouse in Japan.
Second, the building represents one of the earliest reinforced concrete structures in Ehime Prefecture. Some researchers have suggested it may even predate the Bansuisō (1922), which is generally considered Ehime's oldest reinforced concrete building. The dome construction, in particular, employed cutting-edge European building techniques of the era.
Third, as a structure that survived the wartime destruction of Imabari, it serves as an irreplaceable landmark and a tangible reminder of the city's pre-war urban landscape. The building has witnessed the Taishō, Shōwa, Heisei, and Reiwa eras, embodying over a century of local history.
Architectural Highlights and Design Features
The most immediately striking feature of the Imabari Radium Onsen is its silhouette. Depending on the viewing angle, the building presents dramatically different profiles — from the front, the polygonal tower dominates; from the rear, the twin white octagonal domes emerge, giving the building a castle-like or even church-like appearance that seems transported from another time and place.
Recent research by Professor Nishizawa Yasuhiko of Nagoya University Graduate School has revealed that the building was designed with a ship motif. The structure is oriented to face the direction of the Kurushima Strait, as if welcoming visitors from the sea — a fitting tribute to Imabari's maritime heritage as one of Shikoku's first designated open ports for foreign trade.
Inside, the octagonal bathing chambers feature soaring domed ceilings rising over 10 meters high, creating a sense of grandeur reminiscent of ancient Roman thermae. The columns and walls are finished using a sophisticated "marble technique" (マーブル技法) — a masterful plastering method that simulates the appearance of fine marble through skilled craftsmanship. These interiors, though no longer in active use, remain remarkably preserved.
The building also retains its original brick chimney, which adds a distinctive accent to the exterior composition. Research by the University of Tokyo's Institute of Industrial Science, led by Professor Kawaguchi Ken'ichi, has included 3D laser scanning to create detailed digital archives of the dome structures, contributing to the ongoing study and preservation of this architecturally significant building.
Visiting the Imabari Radium Onsen Main Hall
The Imabari Radium Onsen Main Hall is located in the heart of Imabari City, near Imabari City Hall, and is easily accessible on foot from JR Imabari Station (approximately a 15-minute walk). While the building is currently closed as a bathing facility, its remarkable exterior can be viewed at any time. The building's unique silhouette is particularly photogenic, and visitors are encouraged to walk around the entire perimeter to appreciate its changing forms from different angles.
Special interior viewing events are held periodically, offering rare opportunities to see the magnificent octagonal dome ceilings and marble-like plastered interiors up close. Past events have included candlelight illuminations and projection mapping displays that dramatically highlight the building's architectural beauty. The building has also been featured in light-up events coordinated with nearby landmarks such as Nankōbō Temple and the Imabari Public Hall designed by renowned architect Tange Kenzō.
For the latest information on special events and interior viewings, visitors can check the official Imabari Radium Onsen website and social media channels.
Surrounding Attractions
The Imabari Radium Onsen Main Hall serves as an excellent starting point for exploring the rich cultural and natural attractions of Imabari City and the Shimanami Kaido area.
Just a short walk away is Nankōbō Temple, the 55th temple on the Shikoku 88 Temple Pilgrimage and the only temple in the circuit bearing the name "bō" (坊). Originally established as a branch of Ōyamazumi Shrine on Ōmishima Island, Nankōbō features a 300-year-old camphor tree designated as a city natural monument.
Imabari Castle, built in 1604 by the master castle builder Tōdō Takatora, is another must-see. One of Japan's rare sea castles with seawater drawn into its moat, the reconstructed five-story keep offers panoramic views of the city and the Seto Inland Sea.
The Shimanami Kaido, connecting Imabari to Onomichi in Hiroshima Prefecture, is one of Japan's most celebrated cycling routes, offering breathtaking views of the island-studded Seto Inland Sea across approximately 60 kilometers of bridges and island roads. The Kamerojima Observatory on Ōshima Island provides particularly stunning panoramic views of the Kurushima Strait and its three-span suspension bridge.
For those interested in Imabari's famous towel industry, the Towel Museum offers interactive exhibits on towel manufacturing, towel art displays, and a well-stocked shop featuring products from the region's leading manufacturers.
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Q&A
- Can I go inside the Imabari Radium Onsen Main Hall?
- The building is currently closed as a bathing facility and is not open for regular interior visits. However, special interior viewing events are held periodically, during which visitors can see the magnificent octagonal domed bathrooms and marble-like plaster interiors. The exterior can be viewed freely at any time. Check the official website and social media channels for upcoming event announcements.
- How do I get to the Imabari Radium Onsen Main Hall?
- The building is located approximately 1 kilometer northeast of JR Imabari Station, about a 15-minute walk. It is situated in the Kyōei-chō district near Imabari City Hall, in the central area of the city. By car, it is about 10 minutes from the Imabari IC on the Shimanami Kaido expressway.
- Why is it called "Radium Onsen"?
- The name reflects the Taishō-era fashion of "radium baths," which were popular in the early 20th century when radioactive elements were widely believed to have therapeutic health benefits. The facility was originally part of a larger entertainment complex called "Kyōrakukan" and received the name "Radium Onsen" in 1927 when the bathhouse became an independent facility.
- What makes this building architecturally significant?
- The building features an extremely unusual combination of geometric forms: a tower with pentagonal and hexagonal layers, twin octagonal domed bathrooms, and a brick chimney. It is one of the earliest reinforced concrete structures in Ehime Prefecture and employed cutting-edge European dome construction techniques. Recent research has also revealed that the building was designed with a ship motif, oriented toward the Kurushima Strait.
- How did the building survive the Imabari air raids?
- While approximately 80% of central Imabari was destroyed in the 1945 air raids, the Radium Onsen's sturdy reinforced concrete construction helped it withstand the firestorm. The building had already been serving a military role as the headquarters of the local homeland defense corps. After the raids, it became a critical hub for the city's recovery, housing temporary hospitals and banking facilities on its upper floors.
Basic Information
| Name | Imabari Radium Onsen Main Hall (今治ラヂウム温泉本館) |
|---|---|
| Cultural Property Designation | Nationally Registered Tangible Cultural Property (Building) — Registered November 29, 2016 |
| Construction Period | Taishō era (1919–1926), renovated in 1988 |
| Structure | Reinforced concrete, 2 stories, with tower and chimney; building area 408 m² |
| Founder | Murakami Kanzō (村上寛造) |
| Owner | Radium Onsen Co., Ltd. (株式会社ラヂウム温泉) |
| Address | 4-2-8 Kyōei-chō, Imabari City, Ehime Prefecture 794-0024 |
| Access | Approximately 15 minutes on foot from JR Imabari Station; about 10 minutes by car from Imabari IC |
| Current Status | Closed as a bathing facility (since March 2014); exterior viewable at all times; interior viewings during special events only |
| Official Website | https://imabari-radium.com |
References
- 今治ラヂウム温泉本館 — 文化遺産オンライン
- https://bunka.nii.ac.jp/heritages/detail/273582
- 国指定文化財等データベース
- https://kunishitei.bunka.go.jp/heritage/detail/101/00011425
- 平和とまちのシンボルとして後世に 国登録有形文化財『今治ラヂウム温泉本館』— iyomemo
- https://www.iyobank.co.jp/sp/iyomemo/entry/20201105.html
- 今治ラヂウム温泉 — Wikipedia
- https://ja.wikipedia.org/wiki/今治ラヂウム温泉
- 今治から放たれる希望の光、今治ラヂウム温泉本館ライトアップ — 今治タオル公式ブランドサイト
- https://www.imabaritowel.jp/imabari_life/imabari/imabari_life/imabari4777
- まちの100年を見てきた建物「今治ラヂウム温泉本館」— 四国電力広報誌 ライト＆ライフ
- https://www.yonden.co.jp/cnt_landl/2103/report.html
- 今治ラヂウム温泉本館 — 愛媛県教育委員会
- https://ehime-c.esnet.ed.jp/bunkazai/kennobunkazai/tourokubunkazai/touroku-kohyo/radiumuonsen.htm
Last verified: 2026.04.04