A large number of Onsen has been used as therapeutic baths or a cleansing place for pilgrimages before they visit shrines in Nanki Kumano since the old days. The Shirahama Onsen, Tsubaki Onsen, Katsuura Onsen and Yukawa Onsen use natural hot spring developing from long ago. The Shirahama Onsen (Muro-no-yu) is ranked as Japan’s three oldest hot springs and Japan top three largest hot springs for the hot spring has been enjoyed from the Asuka period (around the 7th century). Yukawa Onsen is one of the spas which has the oldest history in the Wakayama prefecture continuing from the end of the 5th century. The Tsubaki Onsen and Katsuura Onsen has been here from the Edo Period. These Onsens are said to have started in an area along the Kareginada arc-shaped dike and the Kozagawa arc-shaped dike.
Spa of Saki（Shirahama Onsen）
Katsuura Onsen
There are no recent volcanos in the Kii Peninsula, but numerous Onsens are gushing. It has long been discussed about the heat source of the Onsen. Previously, it was thought that the excess heat of the magma, which formed the Arcurate Dikes of Kozagawa and Karakinada, had caused the high temperature fluid to rise and gushed out from between the cracks. However, recent studies shows that the high temperature fluid due to dehydration of the subducting plate had risen through the dike rocks and surrounding cracks, and gushed out. The hot water of the Onsen is effective for your health, so Emperors visiting Kumano in the past had dropped by as well as feudal lords taking a respite here.
