箱根温泉ガイド

Sengokuhara is thought to have once lain beneath Lake Ashi. A steam explosion at Mount Kamiyama reshaped the land, and when the water drained away this broad marsh was left behind. The pampas grass that turns the plain gold each autumn grows on that old lakebed.

It is flat and open, but it was never blessed with hot water of its own — springs do not conveniently rise on a plateau at 700 metres. So people looked to Owakudani, the steaming volcanic valley above, and set about bringing its water down. Attempts began in the mid-Edo period, and in 1736 the channel finally worked.

Delivering water reliably over a mountain was another matter with the technology of the time. Sengokuhara only came into its own as a hot-spring district in the Meiji era, and from the early Showa years it grew as a district of summer villas.

Today Sengokuhara draws on 32 sources, with water at 70°C and a flow of 3,212 litres per minute. The clouded sulphur water of Owakudani and the clear water of Ubako are centrally managed and distributed to the inns — which is why two baths in the same village can be quite different colours.

The springs are calcium sulphate (gypsum) and simple sulphur springs of the hydrogen-sulphide type. Gypsum water is gentle and leaves the skin settled and soft; sulphur water carries its distinctive scent and clouds to white. That sulphur is why Sengokuhara is known as the village of the milky bath.