Hotel Iya Onsen is a solitary inn perched on the cliff edge of the deeply carved V-shaped Iya Valley in Miyoshi City, Tokushima Prefecture. Iya Onsen is counted among Japan''s Three Great Secret Hot Springs, alongside Niseko Yakushi Onsen in Hokkaido and Yachi Onsen in Aomori Prefecture. The hot spring was drilled in 1965, and the hotel opened in 1972. It is a member of the Japan Association of Secluded Hot Spring Inns and is the only member establishment in all of Shikoku.

The spring water is classified as an alkaline simple sulfur spring with a pH of 9.1. The source temperature is approximately 38 to 39 degrees Celsius, close to body temperature, making it an exceptionally rare natural free-flowing hot spring in Shikoku. The water contains sodium, calcium, chlorine, carbonate, and sulfur compounds. Its high alkaline content dissolves old skin cells, earning it the reputation of a beautifying spring. The water has a distinctive silky texture with fine bubbles that cling to the skin, and white mineral deposits floating in the bath are evidence of the natural spring source.

The hotel''s most iconic feature is the open-air bath located at the bottom of the gorge, reached by a cable car that descends 170 meters at a 42-degree angle over approximately 5 minutes along a 250-meter track. The two outdoor baths, Keikoku no Yu and Seseragi no Yu, alternate daily between men and women. A new cable car vehicle was introduced in spring 2023. The hotel also features an indoor panoramic bath called Unyu Tenku no Yu (SORANOYU), renovated in 2021 as an infinity-style bath overlooking the Iya Valley mountains. The outdoor baths use natural free-flowing source water, while the indoor panoramic bath is heated and uses a circulation system. Day-trip bathing costs 2,000 yen for adults for the outdoor bath including the cable car, or 700 yen for the panoramic bath only. The hotel has 17 guest rooms with overnight stays starting from 20,130 yen per person with two meals.