Kiriake Onsen is located in the innermost reaches of Akiyamago Valley, Sakaemura, Shimo-Mochi-gun, Nagano Prefecture, nestled in a deep gorge along the Nakatsugawa River at an elevation of approximately 870–900 meters. Surrounded by 2,000-meter-class peaks including Mt. Naeba (100 Famous Mountains) and Mt. Torikabuto (200 Famous Mountains), this is one of Japan's most remote and celebrated hidden hot spring destinations.

The defining feature of Kiriake Onsen is its unique riverside wild spring experience: visitors use shovels to dig into the riverbed of the Nakatsugawa River's left bank, where hot spring water naturally bubbles up at temperatures exceeding 50°C. By channeling cold river water into the hand-dug pool, guests can craft a perfectly personalized outdoor bath—a wild and creative bathing style that has captivated hot spring enthusiasts across Japan.

The history of Kiriake Onsen dates back to around 1700, when Shimada Sanza'emon, the local village headman, discovered the spring. The oldest surviving written record is from Kyōhō 7 (1722), and organized facilities for therapeutic bathing guests (tōji) were established beginning in Kansei 4 (1792). After the facilities were destroyed by floods in the late Edo period, they were revived in 1972 when the village-operated Yukawakaku reopened. The Edo-era literary figure Suzuki Bokushi famously praised this place as a "paradise" (桃源郷) and a "cleansing of the soul" (命の洗濯), helping to spread Akiyamago's fame to the wider world. The area also carries the legend of Heike (Taira clan) refugees who are said to have settled here after their defeat around 1185–1189.

In terms of popularity, Kiriake Onsen draws family visitors and young couples for summer river play, and autumn foliage enthusiasts in fall. It is widely celebrated among Japan's onsen connoisseurs, earning an extraordinary atmosphere score of 4.50 on travel review sites. However, the area is a heavy-snowfall zone (豪雪地帯), and road closures in winter make spring through autumn the recommended visiting season.

Currently, three lodging facilities operate along the Nakatsugawa River: Kiriake Riverside House, Hiky ō no Yado Yukiakari (a member of the Society to Protect Japan's Hidden Hot Springs), and Kiriake Onsen Yukawakaku (currently closed for renovation).