Chubu Ito, Shizuoka
KAI Ito
Name in Japanese. Look for this on the sign, or show it to a taxi driver.
Onsen ryokan (Hoshino Resorts KAI), for staying guests. Hot-spring inn. See the official page for spring details.

Tattoo rule
What the official page says
私たちは、お客様の文化背景や価値観を尊重し、刺青・タトゥーをされているお客様の利用を制限しておりません。 しかしながら、すべてのお客様が快適にお過ごしいただけるよう、他のお客様が恐怖心を抱く可能性があると私たちが判断した場合、温泉・大浴場のご利用をお断りする場合がございます。
We respect our guests' cultural backgrounds and values and do not restrict guests with tattoos. However, so that everyone is comfortable, we may refuse use of the hot spring or large bath if we judge that other guests could feel afraid.
Hoshino Resorts' group FAQ says it does not restrict guests with tattoos. Staff may still refuse the baths if they judge other guests could feel afraid.
This is a group-wide rule from Hoshino Resorts. KAI inns serve staying guests, so the no-restriction rule applies.
Where it is
Chubu region, Shizuoka prefecture. About 29 km in a straight line from Hakone.
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Rules can change. Check the official page on the day you go. Any paid link is labelled next to the button. We have not visited this bath ourselves.