A day spa perched on a bluff with the whole Pacific in front of it — both the rotenburo and the sauna face the sea, giving sunrises in the morning and fishing-boat lights at night. Carbonated bath, stone sauna and restaurant; open 9 am to 1 am. ¥950 on weekdays. About 10 minutes by car from Hitachi-Taga Station on the JR Joban Line, doable as a day trip from Tokyo.
Two hours by train from Tokyo, a day spa right in front of Oarai Sun Beach. The open-air baths — 'Kuroshio' for men, 'Oyashio' for women — look straight out over the Pacific, and the strong salt water from 1,500 m down keeps you warm long after. There's also a carbonated bath. The panoramic restaurant serves seafood from Oarai port. ¥1,000 on weekdays, 10:00–21:30, open daily. Five minutes by taxi from Oarai Station.
About 90 minutes from Akihabara via the Tsukuba Express, a day spa on the slopes of Mt. Tsukuba. The open-air bath opens onto a cliff with the whole Kantō plain below—the classic post-hike or post-cable-car soak. Alkaline simple spring water around pH 9 leaves skin smooth. ¥1,100 weekdays, ¥1,300 weekends; reservable private baths too. Check the calendar for closure days.
A long-established hotel on the cliffs of the Izura coast, the scenic spot beloved of art historian Okakura Tenshin. The main building and the Taikansō annex flank the Rokkakudō pavilion; day bathers use Taikan-no-yu in the annex. The open-air bath, refurbished in 2012, sits right above the Pacific — free-flowing spring water, the horizon and the sound of breaking waves. The indoor hall also looks out to sea through big windows. Day use in two sessions, 11:00–15:00 (last entry 14:30) and 18:00–21:00 (last entry 20:30), ¥1,100. Closure days are irregular, so check the official notice page. Five minutes by car from JR Ōtsukō Station; combine with the Tenshin Memorial Museum and Rokkakudō.
A public-run hot-spring hotel on the clear Kuji River in Daigo, Ibaraki — the town of Fukuroda Falls. The main bath has an indoor tub and sauna, and from autumn to winter (Sep–Jan) it becomes the famous 'apple bath', floating with local apples. Day use 11:00–20:00 (last entry 19:30), ¥800 for adults including a face towel; open daily. A private barrel sauna (¥3,300 / 90 min, reservation), a post-bath lounge and a 16-hole ground-golf course in the garden are also available. About 10 minutes by taxi from Hitachi-Daigo Station and 15 minutes by car from Fukuroda Falls — easy to combine with the falls or apple picking.
A town-run day spa on a rise above the Kuji River in Daigo, Ibaraki, the town of Fukuroda Falls, one of Japan's three great waterfalls. The alkaline simple water is soft; there is a large indoor bath with a waterfall-massage and bubble bath, and the pride of the place is an open, airy outdoor bath with a sweeping view of the Yamizo hills and the river — especially fine in autumn colour. Sauna, rest room, Japanese restaurant and shop, used equally by locals and visitors. Adults ¥710 on weekdays, ¥1,010 on weekends and holidays (¥500 after 17:00), children ¥350/¥500; open 10:00–20:00 (last entry 19:30), closed the 1st and 3rd Wednesdays and December 31. Soap and shampoo provided, towels sold. About 15 minutes by bus from JR Hitachi-Daigo Station to 'Mori-no-Ideyu'; about an hour by car from Naka IC. Combine with Fukuroda Falls and the local shamo chicken cuisine.
A municipal day spa in the Suifu district of Hitachiōta, Ibaraki, near the Ryūjin Great Suspension Bridge, famous for Honshū's highest bungee jump at 100 m. It fills with visitors combining it with the gorge's autumn colours or carp-streamer festival, plus locals. There are two bathrooms — one with an open-air bath, one with a sauna — swapped daily between men and women, so check ahead if you want the open-air side. The clear, soft simple spring is known for warming you well. Adults ¥800 on weekdays, ¥1,000 on weekends and holidays; children ¥400/¥500; cheaper after 16:00. Open 10:00–20:00 (last entry 19:00), closed Tuesdays and Wednesdays (the next business day if a holiday) and December 29–January 3. Restaurant (the mapo tofu is popular), rest room and 70 parking spaces. About 50 minutes by car from Naka IC, or by city bus from JR Hitachi-Ōta Station to 'Keganorokku' then 4 minutes on foot. A handy waypoint on a northern-Ibaraki drive with Fukuroda Falls and Oku-Kuji.