Located in Shirahama Town, Nishimuro County, Wakayama Prefecture, Saki-no-Yu is one of Japan's oldest hot springs. Shirahama Onsen is counted among Japan's Three Ancient Springs alongside Dogo Onsen in Ehime Prefecture and Arima Onsen in Hyogo Prefecture, and Saki-no-Yu has been known since the Asuka and Nara periods over 1,400 years ago. Formerly called Muro-no-Yu, it is mentioned in the Nihon Shoki (Chronicles of Japan) and the Man'yoshu poetry anthology. Many emperors and members of the Imperial court, including Emperors Saimei, Jito, and Monmu, visited these springs for therapeutic bathing. It is the only surviving hot spring among the Seven Yuzaki Hot Springs recorded in the Nihon Shoki. The open-air bath is built on rocky shores where Pacific Ocean waves crash against the rocks, offering an extraordinary sense of unity with the sea. The natural hollows in the sandstone that served as bathing pools in ancient times are preserved to this day. The spring water is a sodium chloride spring with a source temperature of 78°C, sourced from the Miyuki (Imperial Visit) spring. The water is clear with a moderate salty taste and is supplied as free-flowing kakenagashi with complete daily water replacement. Shampoo and soap are prohibited as the water flows directly into the ocean. Admission is an affordable 500 yen for ages 3 and older.