Zaō Onsen (蔵王温泉) is a famous hot spring area on Mount Zaō in the northern part of Honshū, the main island of Japan. Records date back as far as 110 AD. A wounded warrior is said to have drawn an arrow out of his body and cleaned the wound at a spring only to find that the injury healed miraculously quickly and well.
The sulfur springs of Zaō Onsen smell of rotten eggs, which only connoisseurs know to appreciate, and which saves Zaō from being overrun by tourists. Although Mount Zaō stretches between Yamagata and Miyagi Prefectures, the town where Zaō Onsen is located was recently merged into Yamagata City. The hot spring is accessible via the Tōhoku Expressway.