Youroukeikoku Onsen Kiyomoto

Located in Tozura, Ichihara City, Chiba Prefecture, in the mountains along the Yoro River, Kiyomoto is a small "black-water" inn in the Yoro Valley hot spring area, about a 20-minute walk from Youroukeikoku Station on the Kominato Railway. Its own source spring rises right in front of the entrance, and the inn describes it as bubbling up continuously without pause, an unusually close relationship between building and source.

The water is classified as a sodium chloride-bicarbonate spring with a pH of 8.2, an alkaline cold mineral spring. The source temperature is only 17.8°C, with a flow rate of about 12.8 liters per minute, so the water is heated before reaching the baths. Rich in iodine, it takes on a deep, glossy dark color that gives the bath its nickname "kuroyu" (black water), prized for leaving skin feeling smooth. Because the operator has not disclosed whether the water is diluted, circulated, or chemically treated, it cannot be described definitively as a pure source-fed flow-through bath.

The bathing facilities consist of separate indoor baths for men and women plus a reservable family bath; there is no open-air bath. The inn has only nine guest rooms. In September 2023, Typhoon No. 13 caused the Yoro River to flood, submerging the ground floor to a depth of over 1.7 meters, but after repairs — including retiled bathing areas — Kiyomoto reopened in September 2024. Since July 2022 the inn has operated as a stay-only property and no longer offers day-trip bathing.