Oku-Shiobara Arayu Onsen is a hidden hot spring resort located in a mountainous area at an altitude of approximately 970 meters, one of the 11 Shiobara hot springs and one of the 4 Oku areas of Tochigi Prefecture. It was born in the Manji 2 (1659) great earthquake when the source of Motoyu Onsen was buried and new hot springs emerged from the Arayu explosive crater. The place name "Arayu" (new hot spring) was given meaning "hot spring newly opened by the residents of Motoyu," and later the meaning "deep in Shiobara Onsen" was added to become the current "Oku-Shiobara Arayu Onsen." Records show that it was bustling with hot spring therapy visitors during the mid-Edo period, making it a historic hot spring resort with over 360 years of history.

Steam and sulfur odors still rise from Sulfur Mountain (explosive crater remains), and it is located on the highest plateau in Shiobara, blessed with the rich nature of Shiobara Onsen in Nikko National Park. The unique landscape with former sulfur mining remains visible in the background is also characteristic. Currently, there are three traditional communal baths called "Naka-no-yu," "Tera-no-yu," and "Mujina-no-yu," maintaining the atmosphere of a hot spring therapy resort and enjoying high popularity among hot spring enthusiasts as a hidden hot spring. The cloudy white sulfurous hot springs are truly authentic hot springs where many regular visitors come, known as a rare hot spring resort where you can enjoy bathing in the beautiful natural air.