6 Facilities
A terraced open-air bath along a mountain stream that holds 200 people, with bluish-white strongly acidic sulfur water. Open late April to late November only; closed in winter. Summer starlight sessions at night.
A log-cabin-style communal bath at the top of Takayu-dōri. Zao's three public baths (Kamiyu, Shimoyu, Kawarayu) all cost ¥200, paid into an honesty box. No washing stations — just rinse and sink into the strongly acidic milky sulfur water.
One of the three public baths of Zao Onsen, set quietly up the Yu-no-Ka lane. It is a 'foot-of-the-spring' bath where water rises directly beneath the slatted floor, with no added water and no recirculation — a full flow-through. Open 6:00–22:00 with no closing day, it is unmanned: you put ¥300 (¥100 for children) in the box at the entrance. There are no showers or taps, only a rinse before entering, but the strongly acidic sulphur spring is exactly as it comes from the ground. It is run by the Zao Onsen tourist association, and inns in Zao sometimes hand out free bathing vouchers.
A wooden public bathhouse in the heart of Zao Onsen in Yamagata City, a spa said to have been opened 1,900 years ago. Zao has three communal bathhouses - Kamiyu, Kawarayu and Shimoyu - long used by locals and long-stay cure guests. Zao's water is among Japan's most strongly acidic sulfur springs (around pH 1); Shimoyu blends the Jaaragawa-Orikuchi, Inkyo and Kaminokawa sources in full free-flow. Because the water barely meets air, it stays clear rather than milky. An unmanned style - drop coins in the red box at the entrance - with simple gender-separated indoor tubs, no showers, just ladle-water for rinsing. At 300 yen it delivers Zao's intense spring water straight, and many rate it the most quintessentially Zao of the three bathhouses. A lukewarm footbath adjoins. About 3 minutes on foot from the Zao Onsen Bus Terminal, open 6:00-22:00 year-round.
A day-bathing-only open-air facility beside the spring-fed stream just below the Zao Onsen Grand Open-Air Bath in Yamagata City. Its motto is always the first-bath welcome, and the tubs - fed by some of Zao's most abundant flow - pride themselves on spotless cleanliness. The water is Zao's signature strongly acidic sulfur spring (acidic, sulfur-bearing aluminum sulfate-chloride), free-flowing; praised for joint pain and skin troubles, it is also known as a beauty-skin bath. The spacious rotenburo offers autumn foliage by day and light-ups by night, with yunohana drifting through the milky water. Admission is 550 yen for junior high and up, 300 yen for elementary, free for preschoolers; open 10:00-19:00 (Wednesdays from 14:00). A few minutes by car from the Zao Onsen Bus Terminal - a fine companion to a communal-bath tour.
An inn right in front of the Zao Onsen Bus Terminal in Yamagata City, running 100% free-flowing water from its own self-springing source - a certified natural-hot-spring display facility of the Japan Spa Association. That source feeds the main bath, the open-air bath and all four private baths: a lavish use of water. The bath is Zao's classic milky, strongly acidic sulfur spring, and the sulfurous halls live up to the inn's name - enjoying onsen through the five senses of sight, touch, scent, sound and taste. Day bathing runs 12:30-17:00 (last entry 16:30) at 800 yen for adults and 400 yen for ages 3-12, covering the indoor and open-air baths. The four characterful private baths are available for 2,500 yen per 50 minutes (12:00-17:00, until 15:00 when crowded). An ideal base for the Zao Ropeway and the communal-bath tour, with free parking for 30-40 cars.