Washing Body First (体を洗ってから入る - Karada o arau)
The absolute golden rule of Japanese hot springs (onsen) and public baths (sento): you must thoroughly wash and rinse your entire body at the washing stations before entering the communal bath water.
Rooted in Shinto/Buddhist concepts of physical purification. Since the hot spring water is a shared resource, washing beforehand ensures the thermal spring remains completely clean and hygienic for all bathers.
Upon entering the bath area, head straight to the washing stalls first. Sit on the provided small stool, lather up with soap and shampoo, and rinse off all bubbles completely before stepping into the tub.
What is the absolute first action you must take before stepping into a Japanese communal bath?