Maga Onsenkan is a rustic wooden communal bathhouse nestled in a mountain valley along a tributary of the Asahi River in Maniwa City, Okayama Prefecture. Its history spans approximately 700 years, with legends dating back to the era of Emperor Go-Daigo (1318-1339), when a wounded samurai defeated in the Battle of Senjozan in Hoki Province is said to have healed his injuries here. During the Edo period, the lords of the Katsuyama and Tsuyama domains visited for therapeutic bathing, draping curtains (maku) around the bath for privacy — giving the famous Maku-yu its name. The spring was ranked as the third maegashira on the west side in the National Therapeutic Hot Spring Rankings published in 1980.

The water is classified as alkaline simple hot spring with a pH of 9.4, a source temperature of approximately 39.5 degrees Celsius, and a natural flow rate of 205 liters per minute. The most remarkable feature is the foot-welling source — hot spring water rises directly through cracks in the bedrock at the bottom of the bath. The water is colorless, transparent, and nearly odorless, with a silky smooth texture on the skin. It is completely free-flowing from the source with no added water, heating, or recirculation.

The facility consists of Maku-yu (mixed-gender rock bath), separate men''s and women''s baths, and three private baths. Maku-yu is remarkably compact at approximately 1.6m by 2m — often called Japan''s smallest mixed bath — with a depth of about 1.2m requiring bathers to stand. Spring water flows in through bamboo pipes while bubbles rise from cracks in the bedrock. Admission is 250 yen for adults and 100 yen for children (regular bath), 400 yen for adults and 200 yen for children (Maku-yu), or 1,300 yen for a private bath (up to 3 people). Open 8:00-21:00 (last entry 20:10), closed Tuesdays.