Osato Onsen Saitama

Osato Onsen Saitama is a hot spring in the Osato district of Kumagaya, a city in northwestern Saitama Prefecture, Japan, notorious throughout Japan for recording the country's highest reliably measured air temperature — 41.1°C in 2018 — in what is called the 'Kumagaya phenomenon,' where trapped Pacific heat and Fohn effects from the Chichibu mountains combine to make this city Japan's unofficial 'hottest place.' The naturally bicarbonate-rich spring waters here offer a gentle, alkaline therapeutic soak valued for their skin-softening and digestive-supportive properties, providing a restorative mineral bathing counterpoint to the extreme summer temperatures that define Kumagaya's climate. The remarkable juxtaposition of Kumagaya's identity as Japan's temperature record holder with the restorative pleasures of soaking in naturally warm but therapeutically balanced bicarbonate mineral spring waters gives Osato Onsen a uniquely memorable character.