Beppu Hot Spring town in Oita Pref. has the largest volume of hot water in Japan. There are as many as about 3,000 hot spring sources around the areas known as “Beppu Hatto (eight major hot springs)” including Kankaiji, Kanawa and Kamegawa. Also the tour called “Jigoku Meguri (Hell Tour),” through which you will go around the eight Jigokus (geothermal pits) such as Umi Jigoku (Sea Hell), Yama Jigoku (Mountain Hell) and Kamado Jigoku (Cooking Pot Hell), is a very popular sightseeing program. Umi Jigoku is the largest Jigoku of the eight. Although the water temperature is as high as 98℃, its cobalt blue water remind us of the sea in the South Pacific Ocean. This hot spring pond emerged about 1200 years ago after Mt. Tsurumi erupted. When iron sulfate content reacts to the sun light, the water looks blue. Contrary to the name of “Jigoku,” its bottomless cobalt blue is really beautiful.