Kojigoku Onsenkan is a public bathhouse situated in the Kojigoku district, approximately 1.5 kilometers from the center of Unzen Onsen. Established as a therapeutic bathing facility in 1731 during the Kyoho era, the site was reportedly visited by the late-Edo period intellectual Yoshida Shoin. The bathhouse opened as a public facility in 1919 and was rebuilt to its current form in 1993. The water is a simple sulfur spring of the hydrogen sulfide type, emerging at 51.1 degrees Celsius with a mildly acidic pH of 4.3. Located directly above the source, the bathhouse receives freshly risen milky-white sulfur water with no intermediary, offering an exceptionally pure bathing experience. The wooden structure, darkened over decades by sulfur deposits, and the high-ceilinged bathing hall evoke the atmosphere of a mountain retreat. Two pools are available: a hotter one at 43 degrees and a cooler one at 40 degrees. Enveloped in the scent of sulfur, the opaque white waters are reputed to benefit neuralgia, poor circulation, chronic skin conditions, diabetes, and hypertension. The bathhouse is widely considered the finest nigori-yu cloudy bath in all of Unzen.