Zao Onsen Dairotenburo, Yamagata

Zao Onsen Dairotenburo is a large open-air bath situated along a mountain stream in the Zao Onsen hot spring area of Yamagata Prefecture. The hot spring resort itself has a history spanning approximately 1,900 years, reportedly discovered in 110 AD by Kibino Tagayu, who accompanied the legendary hero Yamato Takeru on his eastern expedition. The hot spring town sits at an altitude of 880 meters above sea level on the slopes of volcanic Mount Zao, making it one of the oldest onsen resorts in Japan's Tohoku region.

The Dairotenburo features an expansive bathtub built with accumulated natural stones, large enough to accommodate 200 people simultaneously. The bath is positioned in a small valley surrounded by forest, accessed via a long series of stairs through the woodland. The water comes from a natural sulfur spring with strong acidity, recognized as one of Japan's most acidic hot springs. The water is excellent for softening and whitening the skin, and visitors should note that metal accessories must be removed before bathing due to the highly acidic nature of the spring. The facility is notably tattoo-friendly, welcoming visitors with body art.

Visitors experience bathing in a completely open construction surrounded by Zao's natural mountain environment, creating an immersive connection with the forested valley setting. The mineral-rich waters and remote forest location provide a tranquil bathing experience that has been enjoyed for centuries.

The bath can be reached from JR Yamagata Station by taking a Yamagata Kotsu bus to Zao Onsen bus terminal. The bus journey takes approximately 40 minutes and costs around 1,000 yen for adults and 500 yen for children. Admission to Zao Onsen Dairotenburo is 800 yen for adults and 400 yen for children aged 1-11 years. The facility is closed from late November to mid-April due to winter conditions.