Toyama · Imizu & Shinminato
Kaiō Natural Onsen, Imizu
天然温泉 海王（射水・道の駅カモンパーク新湊隣）
A day spa beside the 'Kamon Park Shinminato' roadside station in Imizu, on Toyama Bay. Its spring is a dense chloride water said to rank among the richest in Japan in dissolved minerals, with several times the free carbon dioxide of shop-bought bath fizzers, so onsen enthusiasts know it as a genuine carbonated chloride spring. The tea-brown, salty, iron-rich water warms you deeply; there are indoor and open-air baths, a sauna and a cold plunge. What stands out is the long day: an early-morning bath from 05:00 through to midnight (23:00 on Sundays), with cheaper early and late rates. Regular admission is ¥970 for adults (¥1,020 weekends and holidays), ¥750/¥780 early or late, ¥520 for children. Closed Mondays (open if a holiday, then closed the next weekday) and January 1. Easy to pair with the Shinminato Bridge, Kaiwo Maru Park and seafood at the Shinminato Kittokito market; about 10 minutes by car from Kosugi IC or 20 minutes by community bus from JR Kosugi Station.
- Price (adult)
- ¥970
- Hours
- 05:00–24:00 (until 23:00 Sun)
- Closed
- Mon (open if a holiday, closed next weekday); Jan 1
- Access
- About 10 min by car from Kosugi IC (Hokuriku Expressway); about 20 min by Imizu community bus (Shinminato–Kosugi line) from Kosugi Station; about 10 min by car from Kosugi (Ainokaze Toyama Railway) or Higashi-Shinminato (Manyōsen)
- Water type
- Simple spring
- Tattoos
- Ask ahead
- Phone
- 0766-82-7777
- Official site
- www.kaiou-onsen.com ↗
- Open in Google Maps
- Google Maps ↗
Essentials
Stay in this onsen town
Compare and book stays in Imizu & Shinminato. Day bathing itself needs no booking.
Opens partner booking site (affiliate)
Why go
- Mineral-dense carbonated chloride spring
- 5 am–midnight; cheaper early and late
- Next to the roadside station; Shinminato seafood
Before you go
- No official tattoo policy is published — ask at reception.
- Last entry is 30–60 minutes before closing.
Features
Sauna & wellness
Price
Who with
Amenities
✔ Verified operating: 2026-09 Yahoo!トラベル（大人970円 土日祝1,020円 朝夜750/780円・5–24時 日曜23時・月曜休 元日休）／アソビュー（旧料金750円）
Prices and hours change. Check official sources before visiting.
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