The 1,300-year-old birthplace of Nasu Onsen. Inside the wooden bathhouse, tubs are graded from 41 to 48°C, all fed with milky, strongly acidic sulfur water. No showers, no soap — start with the traditional head-dousing ritual.
A day-use facility on the same source as Shika-no-yu, open every day until 9 pm with an open-air bath and private rooms. Ideal for families or anyone daunted by Shika-no-yu's rituals — the milky water is identical.
A small riverside hotel on the south side of Kinugawa Onsen, five minutes from Tobu World Square Station. While the big hotels stop day bathing around 15:00, this one welcomes walk-ins 9:00–21:00 for ¥700. Its own alkaline sulfur spring (43.6 °C) flows 100% free into a quirky set of baths: a rotenburo made from an actual Kinugawa river-cruise boat, a rock rotenburo, indoor baths and a swimsuit mixed bath. The slightly cool, silky water is highly rated by onsen fans.
A lone inn at 1,300 m, the last stop in the Nasu hot-spring range. Spring water gushes out behind the building in such volume that it forms a river, dammed into the vast outdoor 'Kawa-no-yu' — nothing else like it in Japan. Mixed bathing since the inn's founding, but bathing wear is included so beginners can relax. Day use is limited to three hours (reception 11:30–14:30), ¥1,300 with face towel and bathing wear. The outdoor bath closes in bad weather or for cleaning, so phone ahead. Autumn colour and snow seasons are the draw.
A city-run day spa in the Kiyotaki valley, between Nikkō's World Heritage shrines and the Irohazaka switchbacks. The all-granite main bath has a sauna and jacuzzi, and the garden-style rock rotenburo looks out to the Nikkō mountains. The alkaline simple spring is clear and silky — a 'beauty bath'. Open 10:00–21:00 (last entry 20:30), closed Thursdays (next day if a holiday) and over New Year. Adults from outside the city pay ¥1,000 (¥500 for residents). The canteen serves soba, udon and other light meals. About 20 minutes by bus from JR/Tōbu Nikkō Station to the 'Yashio-no-yu' stop — a popular finish after Tōshōgū or a trip to Lake Chūzenji and Kegon Falls.
The communal bath of Kawaji Onsen, upstream of Kinugawa on the clear Ojika River. An old cure spa — 'burns to Kinugawa, wounds to Kawaji' went the saying — it uses its own mildly alkaline spring 100% free-flowing with no chlorination. Besides separate indoor and open-air baths there is a mixed rock bath open to the river, where you soak in lukewarm water facing the stream and hills (bathing garments allowed). A low-temperature sauna, private bath (¥4,000 / 50 min) and rest room complete it. Adults pay ¥1,000 (¥500 for Nikkō residents); open 10:00–20:00 (last entry 19:30), closed Wednesdays (next day if a holiday; open through Golden Week). Fifteen minutes on foot from Kawaji-Yumoto Station on the Yagan Railway, or about 15 minutes by car from Kinugawa-Onsen Station — easy to combine with Kinugawa.
A day-use hot spring in Sekiya, Nasushiobara, near the Yunoka Shiobara roadside station at the gateway to the Shiobara spa valley. The source flows at 68.4°C and 250 litres a minute, so the open-air bath runs 100% free-flowing spring water. The slightly tea-coloured, silky alkaline simple spring is known as a skin-beautifying bath; the indoor pool seats about 20 and the outdoor one about 10, both roomy. There are a sauna, cold plunge, jet lounger and a swimwear spa pool popular with families. Adults pay ¥800 on weekdays and ¥1,000 on weekends and holidays (children 4 to elementary age ¥400/¥500); after 5 pm on weekdays the evening rate drops to ¥600. Open 10:00–22:00 (last entry 21:00), closed the third Wednesday (next day if a holiday). Restaurant, rest room, massage and free parking for 150 cars. About 20 minutes by car from JR Nishi-Nasuno Station or 10 minutes from the Nishinasuno-Shiobara IC on the Tōhoku Expressway – a handy last stop after a drive through the Shiobara gorge or Nasu.