Sakamaki Onsen Kawatsuya is the only hot spring inn on the Niigata Prefecture side of the secluded Akiyama-go region in Tsunan Town, Nakauonuma District, Niigata Prefecture. Located in a scenic spot overlooking the Nakatsugawa Valley, this long-established inn has over 200 years of history. It's also known as the inn where renowned author Eiji Yoshikawa stayed and wrote, retaining a strong atmosphere of a secret hot spring.

The hot spring is a sodium/calcium-chloride/sulfate spring (hypotonic weakly alkaline high-temperature spring) with a source temperature of 39°C, pH 8.0, and a natural flow rate of 13.8 liters per minute. It's colorless, transparent, odorless, with a slight salty taste. The source water flows through naturally, and it's said to be effective for neuralgia, muscle pain, joint pain, sensitivity to cold, and fatigue recovery.

The main feature is 'Meisou-no-yu' (cave bath), which utilizes a natural cave. Hot spring water wells up inside a cave carved from bedrock, allowing bathing in a fantastical atmosphere. For day-use bathing, the cave bath can be used privately by one group at a time (reservation recommended). Another bathing area, 'Tenbou-no-yu' (observation bath), is a viewing bath overlooking the Nakatsugawa Valley, where you can bathe while viewing the magnificent nature.

It's a small inn with 8 rooms total, with warm family-run hospitality as its charm. Meals feature local mountain vegetables and river fish in regional cuisine, allowing you to taste the rich natural bounty of Akiyama-go.

Accommodation rates are 14,070-17,310 yen per person per night with two meals (tax included). Day-use bathing is available for 800 yen for adults and 400 yen for children, with reception from 10:00-14:00 and exit by 15:00. The cave bath is for private use by one group at a time. Check-in is at 15:00, check-out at 10:00, with irregular holidays.

Access is by car from JR Iiyama Line Tsunan Station (about 40 minutes) or from Hokuriku Shinkansen Iiyama Station (about 50 minutes). By car, it's about 90 minutes from Shiozawa-Ishiuchi IC on the Kanetsu Expressway, or about 60 minutes from Toyoda-Iiyama IC on the Joshinetsu Expressway. Free parking is available. As Akiyama-go is a snowy region, studless tires or chains are essential in winter. It's a precious hot spring in a secluded one-inn location where you can enjoy cave bathing and valley scenery.