Okutsu Onsen, located in Kagamino Town, Tomata District, Okayama Prefecture, is one of the celebrated Mimasaka Sanyu (Three Great Hot Springs of Mimasaka) alongside Yunogo Onsen and Yubara Onsen. Its origins are traced to the mythological deity Sukunahikona no Mikoto. During the Edo period, the lord of Tsuyama Domain, Mori Tadamasa, established a private bathing retreat here, attesting to the spring''s esteemed reputation. Towaro was founded in 1928 as a modest three-story wooden ryokan with just ten guest rooms.

The water is classified as alkaline simple hot spring with a pH of 9.2. The source temperature is approximately 41.7 degrees Celsius, and the water contains trace amounts of radon. The most remarkable feature is the foot-gushing source in the underground rock bath, where hot spring water wells up directly through cracks in the bedrock — an exceptionally rare bathing experience found at very few locations in Japan. The colorless, odorless water carries a faint ramune-like tint and has an incredibly gentle, smooth feel on the skin, earning it the reputation of a bijin no yu (beauty bath).

To reach the rock bath, guests descend a staircase and pass through a distinctive plaster-walled tunnel. The small bathing basin, carved from natural bedrock and accommodating about four people, is a luxurious space where natural hot spring water continuously bubbles up from beneath. Currently, overnight stays are suspended, and the inn operates for day-trip bathing only (10:00-16:00) at 1,000 yen for adults. The famous Okutsu tradition of ashifumi sentaku (foot-stamping laundry) utilizes the bleaching properties of the pH 9.2 water and is demonstrated on Sundays and holidays from March through November.