Zao Onsen Large Open-Air Bath is a spacious open-air hot spring located at the far end of the historic Zao Onsen resort in Yamagata Prefecture. Surrounded by dense woodland, the bath offers an immersive experience where visitors can enjoy the natural beauty of the mountains while listening to the sound of a nearby stream and birds singing in the forest.
The outdoor bath is arranged in four large pools on different levels. Together, the pools cover an area equivalent to approximately 100 traditional Japanese tatami mats. The two upper pools are reserved for women, while the two lower pools are for men. The entire facility is large enough to accommodate approximately 200 bathers at the same time.
Built to blend naturally into the surrounding mountain environment, this rustic open-air bath offers a distinctive Japanese bathing experience. Its spacious pools, natural setting, and hot spring water flowing directly from the source are among its greatest attractions.
Zao Onsen is one of the leading mountain resorts in the Tohoku region of Japan, located approximately 40 minutes by car from JR Yamagata Station. The hot spring was formerly known as Takayu or Mogami Takayu, and local tradition dates its discovery back approximately 1,900 years.
The origin of the hot spring is traditionally placed around 110 CE. Today, Zao is known as a year-round mountain resort located next to Zao Onsen Ski Resort. Visitors can enjoy skiing and snowboarding in winter, fresh greenery and mountain walks in spring and summer, and spectacular autumn foliage in fall.
The hot spring town is lined with public bathhouses, day-use bathing facilities, ryokan inns, and hotels, creating the atmospheric streetscape of a traditional Japanese onsen resort. The Sukawa River flows through the town, and upstream stands Sukawa Onsen Shrine, a shrine dedicated to the hot springs.
The Zao Onsen Large Open-Air Bath is located just a few minutes by car from the main hot spring town, deeper in the mountains. Because the baths are surrounded by trees, the experience feels quite different from bathing at an urban spa or hotel.
While soaking in the warm water, visitors can hear the sound of flowing water and birdsong. Sunlight filtering through the trees and the fresh mountain air add to the relaxing atmosphere, allowing bathers to enjoy the hot spring while feeling close to nature.
The surrounding landscape changes dramatically with the seasons. In spring, the area is covered in fresh green foliage, while summer brings the refreshing air of the mountain highlands. In autumn, the trees turn vivid colors, creating the opportunity to enjoy a hot bath surrounded by autumn leaves.
Zao is also famous for its snowy winter landscape. However, the Large Open-Air Bath operates only during a limited season, so visitors should check the latest operating information before planning a visit.
The Zao Onsen Large Open-Air Bath uses 100% natural hot spring water flowing directly from the source. The water is not diluted or artificially heated before being supplied to the baths, allowing visitors to experience the distinctive character of Zao’s mineral-rich spring water.
Zao Onsen is particularly famous for its strongly acidic sulfur spring. The characteristic scent of sulfur is noticeable throughout the area and is an important part of the traditional Zao Onsen experience.
Five natural sources together produce approximately 573 liters of hot spring water per minute. Source temperatures vary depending on the location, ranging from approximately 45°C to 66°C.
The spring is classified as an acidic sulfur-containing aluminum sulfate-chloride spring. Historically, the water has been associated with bathing for various skin-related conditions such as cuts and heat rash, and the area was also once used for collecting the mineral deposits known as yunohana, or hot spring mineral flowers.
Because of its strongly acidic sulfur-rich water, Zao Onsen has long been known in Japan as the “Beauty-Making Bath.” The minerals in the spring water have traditionally been associated with various bathing benefits, making the hot spring particularly popular among visitors seeking a relaxing bathing experience.
Because the water is strongly acidic, however, some people may experience skin irritation. Visitors with sensitive skin should avoid prolonged bathing and adjust their bathing time according to their physical condition.
The Zao Onsen Large Open-Air Bath has no shower facilities, and soap and shampoo cannot be used. Unlike modern spa facilities, the bath is designed primarily for enjoying the hot spring water itself in its natural mountain setting.
Because the strongly acidic water can readily remove oils and other substances from the skin, there is generally no need to scrub the body vigorously. Instead, visitors can experience a more traditional style of Japanese bathing, simply soaking in the mineral-rich water while surrounded by nature.
The appeal of the Large Open-Air Bath extends beyond the properties of its hot spring water. While relaxing in the pools surrounded by trees, visitors can experience the sound of the stream, birdsong, the scent of sulfur, the cool mountain air, and the natural scenery all around them.
The open and spacious baths, surrounded by forest, create a peaceful atmosphere that feels distinctly different from bathing inside a conventional hotel or public spa. It is an opportunity to slow down and enjoy a quiet moment in the mountains of Yamagata.
Zao Onsen Large Open-Air Bath is one of the signature day-use bathing destinations in Zao Onsen, offering visitors the chance to enjoy natural hot spring water in a spectacular mountain setting. The combination of spacious pools, rustic surroundings, and distinctive strongly acidic sulfur-rich water makes it a memorable part of a visit to Zao.
The wider Zao Onsen area offers numerous public bathhouses and accommodation options, as well as seasonal activities such as skiing, snowboarding, hiking, and autumn-leaf viewing. Combining a mountain walk with a relaxing soak in the hot springs is an excellent way to experience the natural landscape and traditional hot spring culture of Zao.
Weekdays 9:30-17:00
Weekends and holidays: 9:30-18:00
Open irregularly (may be closed due to weather conditions)
Open from mid-April to mid-November
Adults 550 yen
Children (under 12 years old) 300 yen
45 min. by bus from Yamagata Station [18km].
30 min. by car from Yamagata Zao IC of Yamagata Expressway [18km].