Located in the mountainous town of Nagato, Yamaguchi Prefecture, Tawarayama Onsen is a historic hot spring said to have been discovered by a white monkey in 916 AD during the Heian period, and it flourished as a directly managed therapeutic bathing site of the Choshu Domain in the Edo period. Machinoyu is the central public bathhouse (soto-yu) located in the heart of the Tawarayama Onsen district. Tawarayama is one of the few remaining onsen towns in Japan where lodgings have no private baths and guests visit communal outdoor bathhouses, preserving Japan's traditional toji (therapeutic bathing) culture, and it is designated as a National Health Resort Onsen. The spring is an alkaline simple hot spring (pH 9.9) with a natural source temperature of 41.3 degrees Celsius, served as flowing fresh source water without dilution, renowned as one of western Japan's finest skin-beautifying waters with its distinctive silky texture.