From Tokyo, Osaka, Kyoto, Fukuoka and Sapporo — real onsen you can do in a day
Combinations that let you keep your hotel and still get a real bath.
From Tokyo
Hakone (85 min by Romancecar) — Tenzan Tohji-kyo, Hakone Yuryo.
Kusatsu (4 h by bus, or 3 h shinkansen + bus) — Gozanoyu, Sainokawara. A long day, but doable.
Ikaho (2.5 h train + bus) — Ishidan-no-Yu.
From Osaka / Kyoto
Arima (1 h by train from Osaka) — Kin-no-Yu and Gin-no-Yu on a combo ticket.
Kinosaki (2.5 h limited express) — bath hopping; on a day trip stick to Ichi-no-Yu and Gosho-no-Yu.
Shirahama (2.5 h limited express) — Saki-no-Yu.
From Fukuoka
Beppu (2 h limited express) — Takegawara, Kannawa Mushi-yu.
Takeo (25 min shinkansen) — Motoyu. The nearest serious onsen.
Kurokawa (3 h highway bus) — three baths on the Nyuto Tegata.
From Sapporo
Jōzankei (60 min shuttle) — Yunohana.
Noboribetsu (1.5 h train + bus) — Sagiri-yu, Dai-ichi Takimotokan.
Universal tip
Last entry is 30–60 minutes before closing. Fix your return connection before you get in.