Kameyama Onsen Hotel

Kameyama Onsen Hotel stands alone on the shore of Lake Kameyama in the heart of the Boso Peninsula, Kimitsu City, Chiba Prefecture. The hot spring was discovered by chance in 1930 during a natural gas drilling operation. After the original source was submerged by the construction of Kameyama Dam in 1972, a new well was drilled at the current site in 1975, and the hotel has drawn its water from it ever since.

The water is classified as a sodium chloride-bicarbonate spring, with a pH of 8.7 (mildly alkaline) and a source temperature of 26.4°C. More than 600 liters flow naturally to the surface every minute from a depth of 2,000 meters, without any pumping. Its deep chocolate-brown color comes from humic substances formed by ancient plant matter decomposing underground, coloring the water so darkly that the bottom of the tub disappears from view. On the skin it leaves a smooth, moisturizing sensation typical of Japan's moor-type springs.

The hotel offers separate large baths for men and women, along with several private open-air baths, each with its own character. The men's bath also includes an unheated pool filled directly with the spring water, letting guests experience it exactly as it emerges from the ground. Day-trip bathing costs 1,000 yen for adults and 800 yen for children, available from 11:30 a.m. to 6:00 p.m. Overnight guests can also enjoy kaiseki-style dinners featuring seasonal Boso ingredients.