Bathing at a sento or onsen
A Kyoto sento is a neighbourhood public bath; an onsen uses natural hot spring water. First time in, “wash first, then soak” covers most of it. Tattoo rules differ from bath to bath, so check before you go.
Sento or onsen?
A sento is a public bath for the neighbourhood, heated water shared by everyone. An onsen is different: much of its water must come from a natural, geothermal, mineral-rich source. A Kyoto sento costs ¥550 a visit for junior-high age and up, ¥200 for primary-school children, ¥100 for infants.
At the door: shoes off, pay first
Take your shoes off at the door and put them in the shoe lockers, then pay at the front desk (bandai). If you have no towel or soap, you can buy them there. Leave valuables at the desk or in a valuables locker.
Undress, separately
Men and women enter through separate doors. In the changing room, take everything off, including underwear, and lock your clothes away with the locker key on your wrist. Tie up long hair so it stays out of the water.
Wash first, then soak
Before you get into a bath, rinse yourself clean: scoop three or four bowls of hot water over your whole body (kakeyu), or wash at the washing area first. Keep your towel and your hair out of the bath water.
In the bath
The water is shared: keep your towel out of the bath, on the rim. No jumping in, swimming or diving, and do not go in drunk. No photos in the bathing area, and keep your voice down.
Tattoos: check first
Tattoo rules vary by bath, so read the bath's own website before you go. Kurama Onsen states that guests with tattoos may use its baths. The Japan Tourism Agency says refusing someone only because they have a tattoo is not appropriate. Some baths ask you to cover a tattoo with a sticker, or suggest a private bath instead.
Sources：京都府浴場組合：京都銭湯 銭湯の利用方法 ↗くらま温泉 公式WEBサイト ↗厚生労働省・観光庁：入れ墨（タトゥー）がある外国人旅行者の入浴に関する対応について ↗観光庁：旅館Q&A（大浴場・タトゥー） ↗日本政府観光局（JNTO）：Onsen Hot Springs — On Tattoos and Etiquette ↗