A new hot spring resort is due to open in the historic ski and spa town of Kusatsu, Japan, in Q2 of 2026.

The forest resort, owned and operated by Hoshino Resorts, will be connected to the town by a private tunnel, exclusively reserved for resort guests.

The new, 94-key property will be managed under Hoshino Resorts' hot spring ryokan brand ‘Kai’ and will trade as Kai Kusatsu.

Located on a hill overlooking the active volcanoes of Mount Kusatsu-Shirane, the hot spring resort will be a 3.5-hour drive from Tokyo’s Haneda Airport and modelled on a traditional Japanese inn, or Ryokan.

Kai Kusatsu, the resort

The new property will have a bathhouse, lounge, courtyard, dining area, shop and a ‘Kai cultural discovery hall’. This space is a feature at other Kai-branded hotels, offering guests the chance to try free activities that celebrate elements of Japan’s regional cultures and crafts. Activities and learning opportunities at this resort will be centred on historical textiles and threads from the local prefecture of Gunma.

The concept for the forest resort, designed by Tatsuro Sasaki Architects, is to blend a nature-rich and peaceful retreat with the vibrant atmosphere of the local hot spring town. The private passage to the town, developed by construction firm Maeda Corporation, will allow guests to experience these two distinct environments.

Maeda Corporation will also build the resort.

The plot for the resort is 111,844sq m and buildings occupy 3,690sq m.

Kai Kusatsu will start taking reservations from Q4 this year.

Last year, Hoshino Resorts announced its debut US resort, a 40-key onsen ryokan in Sharon Springs, New York – which is due to open in 2028.

About the Kusatsu Onsen thermal hot spring

The Kusatsu Onsen, located at the base of the mountain, is one of Japan’s most famous hot springs and one of the leading onsen destinations in the country. It is said to have been a bathing site since the Kofun period (between 300-538AD) and is famous as the place the Samurai went to heal their wounds.

The natural hot spring releases a volume of more than 32,000 litres of water per minute, which is the highest natural release volume in Japan according to the Kusatsu Onsen Tourism Association. The water is too hot to bathe in at the source. Instead, it cools as it flows through the town's open-air hot spring fields, called the Yubatake, before reaching various onsen.

Kusatu's ski industry is busy during the winter, complementing the thermal spa business and is characterised by gentle, tree-lined trails and slope-side restaurants. Zip lines operate in the summer months. The town is located on Japan’s Romantic Road.

Hoshino Resorts' brands

There are 23 properties in Japan operated by Hoshino Resorts under the Kai brand and a spokesperson for the company told Spa Business it plans to have seven more. The hot spring inn theme is coupled with the motto ‘authentic but new’, meaning the brand caters to modern needs, while preserving Japanese aesthetics and traditions.

This will be the first Kai property in the Gunma prefecture and the second property for Hoshino Resorts in the area.

The spokesperson said, "We consider Kusatsu to be an indispensable location for the Japanese hot spring experience and thus aim to promote it not only domestically but also to the wider international audience, especially given that overseas travellers are increasing. Our aim is to contribute to the Kusatsu region by raising its profile and highlighting its attractions for both Japanese residents and travellers from abroad."

Hoshino Resorts also has a number of other brands designed to cater to different markets, which include:

• Luxury hotel brand – Hoshinoya

• Countryside resort hotel brand – Risonare • City tourism hotel brand – Omo

• Free-spirited hotel brand – Beb

About Hoshino Resorts

The company was founded in 1904, when the current CEO’s great-grandfather, Kuniji Hoshino, started a forestry business in Karuizawa. The area was just developing as a holiday destination and in 1914 Hoshino opened a hot spring resort. The property attracted intellectuals, as well as those interested in the region’s rich wildlife.

For years, the resort thrived but when Yoshiharu Hoshino took over the business in 1991 he got to work on expanding the brand.

Since expanding from its original base in Karuizawa in 2001, the company has grown to operate more than 60 properties, with the majority in Japan and additional locations in China, Taiwan, Bali and Guam and soon, the US. It also owns a portfolio of other properties that are managed by other operators, including Hyatt. The company’s shares are traded on the Tokyo stock exchange.

Read our 2014 interview with Yoshiharu Hoshino here.