Where a tattoo is not a problem
Most guides give you a handful of famous names. We read what each facility actually publishes in Japanese and record it — including the places where the shared baths are closed to you but a private bath is not, which is the option almost nobody mentions.
The short answer: go to Beppu
Beppu City publishes its own list of baths that accept tattoos, and the municipal bathhouses on it cost between ¥100 and ¥300. No other city in Japan comes close — in Osaka we could confirm only three out of fourteen, and in Tokyo the large spas almost all refuse entry outright.
Takegawara Onsen
Kaimonji Onsen
Furosen
Ekimae Koto Onsen
Shibaseki Onsen
Horita Onsen
Where else it works
Places with at least four baths we could confirm.
Accepted as you are
No cover-up, no private bath needed — the shared baths are open to you.
Kurama Onsen
Otakinoyu
Gozanoyu
Sainokawara Rotenburo
Tenzan Tohji-kyo
Hakone Yuryo
Gora Hanaougi
KAI Hakone
Niseko Grand Hotel
Mandara-Yu
Goshono-Yu
Ichino-Yu
The private-bath route
The shared baths are closed to tattooed guests, but there is a bath you can have to yourself. Worth knowing: it is not a workaround, it is how a lot of Japanese guests bathe anyway.
Kusatsu Onsen Naraya
Kishigon Ryokan
Hakone Kowakien Ten-yu
Hakone Hotel Kowakien
Hakone Kowakien Mikawaya Ryokan
Hakone Gora Onsen Kinoyu Setsugetsuka
Hakone Suishoen
Hakone Ashinoko Hanaori
Hotel Taisetsu
One thing to watch
There is a difference between “you may not use the baths” and “you may not enter the building”, and Japanese facilities are precise about which they mean. Where the wording refuses entry to the premises, a private bath is not a way around it — we mark those separately, because getting this wrong is how you end up turned away at the door.