Yoro Onsen Honkan is a single-inn hot spring ryokan located along the Fujii River in Minogo-cho, Onomichi City, Hiroshima Prefecture. Established in 1960 (Showa 35), the inn has a unique origin story — the hot spring was accidentally discovered while drilling a well in search of quality water for sake brewing, when mineral water rich in radon unexpectedly gushed forth.

The spring is classified as a simple weak radioactive cold mineral spring (neutral hypotonic cold mineral spring), categorized as a natural radon onsen (silver spring). With a source temperature of 16.5 degrees Celsius, the cold mineral water is heated for bathing. The water is colorless, transparent, and odorless with a mild character, but contains metasilicic acid exceeding standard levels — a natural moisturizing component that gives the water its characteristically soft and skin-friendly quality. Therapeutic indications include gout, rheumatism, neuralgia, and gastrointestinal disorders.

The building has been renovated while preserving the original structure from its 1960 opening, creating an atmosphere steeped in Showa-era retro charm. Nostalgic touches can be found throughout, from the tile-lined bathrooms to the lobby and large communal hall. The inn has 8 Japanese-style and 2 Western-style rooms with a capacity of 30 guests. Day-trip bathing is available for 650 yen per adult from 10:00 to 21:00. A notable feature is that the entire facility operates without municipal water supply, using only the mineral spring water — which is also suitable for drinking — for all purposes.