竜門温泉 is a hot spring town in Oita, Japan. The water leaves the ground at 43–48°C, hot. It measures pH 8.7 — mildly alkaline, the slippery kind. Officially the water is classed as simple spring.
Mild and low in dissolved minerals. Usually clear and gentle on the skin, which is why these baths are often recommended for first-timers.
Figures from the town's Japanese Wikipedia article.
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