Located in Kushimoto Town, the southernmost town on Japan's main island of Honshu, Kobo-yu is a hot spring situated on the Pacific Ocean coastline, just east of the nationally designated Natural Monument Hashigui-iwa (Bridge Pillar Rocks). The name derives from a legend that Kobo Daishi (Kukai), the founder of Shingon Buddhism, appeared in the dreams of ailing villagers to reveal the existence of this hot spring and save them. Originally opened in 1978 as a communal bathhouse, it closed in March 2021 due to declining visitors during the COVID-19 pandemic and was slated for demolition. However, local company OUTDOOR TRIP Co., Ltd. took over the facility, performed a full renovation, and reopened it in autumn 2022 as a private rental hot spring. The water is a simple spring (alkaline) with a notably high pH of 9.5. The source temperature is a cool 27.0 degrees Celsius so it is heated, but it flows freely from a naturally artesian drilled well. The water has a faint sulfur scent and a silky smooth texture with excellent skin-beautifying properties. The semi-open-air bath offers panoramic views of the vast Pacific Ocean and Kii-Oshima island, and overnight guests can enjoy starry skies and sunrise while bathing. The facility operates on a fully reservation-based, private rental system with self-service key access and no on-site staff, providing an intimate hot spring experience. Rated 4.6/5.0 on Nifty Onsen.