I Looked Into Fuji Saiko Onsen Izumi no Yu

I've been slowly researching campsites, day-trip hot springs, and places to stay, and this time I looked at a day-use hot spring in the Saiko area of Yamanashi.

This time it's “Fuji Saiko Onsen Izumi no Yu.” I'm an indoor person and I hardly ever drive, but when I found out it has an open-air bath surrounded by natural rocks and a little library corner, I got curious whether it's a place where I could just relax for a long time.

The Short Version

Besides the big open-air bath surrounded by natural rocks and the “Kuroshio bath,” it even has a library corner and a lawn area, so it looked like a day-use hot spring where you could happily stay long after your bath.
As for Rakuten Mobile signal, the official tool gave it an overall rating of “C.” If you want to rely on your phone once you get there, I'd recommend checking ahead of time.

I've put the details below.

What Kind of Place Is Izumi no Yu?

It's a day-use hot spring facility in the Saiko area of Fujikawaguchiko, Yamanashi Prefecture. When I checked the official website, I couldn't find any information about overnight stays. It seems to be positioned as a place to enjoy bathing, meals, and relaxing.
Here's the basic info I found.

Business hours: These vary by day and are posted on a business-day calendar, apparently. In the September 2026 calendar, the most common hours were 11:00 to 19:00, with some Fridays and Saturdays staying open until 21:00, and a few Sundays opening at 9:00
Regular closing days: I couldn't find an official written rule. In September, the closed days seemed to line up on Tuesdays and Wednesdays
Business calendar for October 2026: At the time I looked, it said “in preparation,” and it seems you need to confirm by phone
Bath fee (weekdays): 900 yen for junior high school students and older, 500 yen for ages 4 to elementary school, and free for ages 3 and under
Bath fee (weekends, holidays, long weekends, and other special days): 1,200 yen for junior high school students and older, 600 yen for ages 4 to elementary school, and free for ages 3 and under
Local member rate: For junior high school students and older living in Minamitsuru District or Fujiyoshida City, you can register (free) and pay 700 yen on weekdays and 900 yen on special days
Payment: Cash only for both bath fees and meals, so credit cards aren't accepted. PayPay can apparently be used only at the shop
Reception: Individual visitors seem to buy an admission ticket from a ticket machine
Parking: Free, with space for regular cars, campervans, and large buses, plus a dedicated wheelchair space. I couldn't find the number of spaces

For directions by train or bus, the official site only has a Google Maps route link and no written explanation that I could find. If you're going by public transport, it looks like you'll need to look it up yourself beforehand.

Komorin

The hours change from day to day, so it seems important to check the calendar before heading out. The October calendar is still in preparation, so I'd probably need to call to confirm.

The Big Open-Air Bath Surrounded by Rocks and the “Kuroshio Bath” Caught My Eye

The star of this place seems to be the big open-air bath built among natural rocks. The water temperature is close to body temperature, and the FAQ apparently says 38°C. There are infinity chairs in the outdoor cooling area, so it looked like a nice place to take it easy after the bath too.

These are the baths introduced for the main bathing area.

Kuroshio bath: It seems to be a bath that features sea minerals
Rotating bath: The theme changes, with things like seasonal scents and herbal baths, apparently
Uttase-yu (falling-water bath): Introduced on the official website
Natural water cold bath: The water temperature is listed as 13.2°C
Sauna: A dry sauna, with the set temperature at 95°C for men and 90°C for women, and no loyly (steam ladling). In the outdoor cooling area, you can apparently use infinity chairs and lie-down beds

I couldn't find detailed information about the spring quality or the source on the official website. As for the benefits, the FAQ seems to list recovery from fatigue and relief from muscle aches.

A Space for Indoor Types That Seems to Have Places to Settle In After Bathing

What interested me most was that it looks like there's plenty to do besides bathing.

Dining hall: About 90 tatami mats in size, and the dishes introduced were conger eel tempura rice bowl, fried chicken, and fried tofu udon (with house-made noodles). The FAQ also seems to mention udon and set meals. I couldn't find prices or hours
Library corner: About 1,000 nature-related books, and apparently picture books and illustrated encyclopedias too. It seems you can use it for resting together with the dining hall
Terrace and lawn area: There's a wooden deck, and you can apparently see the lake from the lawn. Tables and chairs are also provided
Changing room: Spacious, with lockers that have keys, and baby beds on both the men's and women's sides, it seems
Amenities: Shampoo, conditioner, and body soap are provided. A bath towel is 210 yen, a face towel is 160 yen, and a towel set is 350 yen, and it seems toothbrushes (50 yen) and razors (120 yen) are on sale

For groups, there's apparently a private-hire venue called “Yunowa-do” that fits 20 to 100 people. Options like karaoke (5,500 yen per group for 2 hours) and Molkky or table tennis (500 yen per group for 30 minutes each) were also introduced.

Rules Worth Knowing in Advance, Like Tattoos and Outside Food

About tattoos: from 14:00 to 17:00 on each business day, there seems to be a “Tattoo Friendly Time.” During those hours, you can apparently bathe with no extra fee and no reservation. At other times, you can bathe if you cover the tattoo with a cover sticker, and there's no size limit, it seems.

The main points to watch out for were as follows.

Outside food and drinks: Not allowed
Inside the building: Smoke-free, it seems
Changing room and bathing area: Using phones or cameras, doing laundry, and dyeing hair are prohibited
Elementary school students and younger: Must be accompanied by a guardian, it seems
Mixed bathing: Not allowed for ages 7 and up, under a Yamanashi Prefecture ordinance

You can find the details on the official website (https://izuminoyu.hamayouresort.com).

Rakuten Mobile Signal Conditions

I used the official “my Area Connection Simulation” to check this facility's location (Saiko, Fujikawaguchiko). The result was an overall rating of “C.”

If you plan to use your phone a lot inside the facility, or want to follow a map app to get around, it might be reassuring to check ahead of time. That said, phone use is prohibited in the changing room and bathing area, so I don't think you need to worry much about connectivity while bathing.
If you're curious about the signal, you can check your destination beforehand with Rakuten Mobile's official connection simulation tool.

Komorin

The rating was C. It might be a good idea to prepare a little, like saving the directions before you leave.

See Rakuten Mobile Details

Wrapping Up

Looking back over everything, my impression of Fuji Saiko Onsen Izumi no Yu is that it's a day-use hot spring where you could relax for a long time, built around a big open-air bath surrounded by natural rocks and the “Kuroshio bath,” with a dining hall, a library corner, and a lawn area to round it out.

The business hours change from day to day, and the October calendar was still in preparation when I looked. Since payment is cash only, I think it's reassuring to confirm by phone or similar before you visit. As for Rakuten Mobile signal, the official tool gave an overall rating of “C.” If you're curious, please check ahead of time with the official tool.

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