Wakayama · Kumano Hongu Onsen (Yunomine & Kawayu)
Kawayu Onsen Sennin-buro (winter only)
川湯温泉 仙人風呂（冬季限定）
At Kawayu, where 73°C spring water bubbles up through the bed of the Ōtō River, a giant outdoor bath is created every December to February by damming the river. Roughly 50 by 15 metres — big enough for 'a thousand people', as the name says — it's tempered to perfection by the river's cold flow. Free (donation box), 6:30–22:00, swimwear required, open to everyone. Bathing is suspended in bad weather or high water and opening dates shift from year to year. In summer you can dig your own pool in the gravel. Combine with Yunomine and Watarase for the three Hongu baths.
- Price (adult)
- Donation / free
- Hours
- Winter only, 1 Dec – 28 Feb, 6:30–22:00 (start may be delayed; closed when the river is high)
- Closed
- Closed outside the season (Mar–Nov); in season some days are unusable due to weather or water level
- Access
- About 110 min by Ryujin Bus from JR Kii-Tanabe Station to Kawayu Onsen, then 3 min on foot; about 65 min by bus from JR Shingu; 60 min by car from Kamitonda IC
- Water type
- Simple spring
- Tattoos
- Ask ahead
- Admission
- Free (run by the tourist association; donation box). Swimwear compulsory (no nude bathing); bring towel and swimsuit (rentals sometimes available at Kawayu inns or the public bath). Simple changing huts on the riverbank. No shampoo or soap (it is a river). Lit at night. Season: 1 December 2025 – 28 February 2026 (every December–February; the start may be delayed by weather). Closed on days when the water is too cool or the river swells after rain
- Baths
- A giant winter-only outdoor bath roughly 50 by 15 metres, dug into the bed of the Otou river with heavy machinery and dammed with stones — said to hold 'a thousand bathers'. A 73°C source wells up through the riverbed and blends with the stream to around 40°C, hotter in some spots and cooler in others, so you feel your way with your feet. Mixed bathing in swimwear. Every Saturday 20:00–22:00 the 'Yukemuri Toro' lights hundreds of lanterns along the riverbank for a magical night scene. In summer (March–November) the dam is gone, but borrowing a shovel and digging your own private bath in the riverbed is Kawayu's traditional pastime
- Spring water
- Sodium bicarbonate-chloride spring (slightly acidic, pH 6.7, hypotonic), 73°C at the riverbed source, with abundant flow throughout Kawayu. Colourless, almost odourless and soft on the skin — 'natural free-flow' diluted by the river itself. Indicated for neuralgia, rheumatism, fatigue and skin disease. Kawayu, recorded in Edo-period texts, is one of the 'three baths of Hongu' with Yunomine and Watarase, on a rare riverbed where hot water wells up wherever you dig
- Access & parking
- 10 minutes (6 km) by car from Kumano Hongu Taisha, 5 minutes from Yunomine Onsen. By bus (Ryujin Bus / Kumano Kotsu) alight at 'Kawayu Onsen' and walk 3 minutes — about 10 minutes from Hongu Taisha-mae, about 2 hours from JR Kii-Tanabe, about 1 h 10 min from JR Shingu. Free parking for about 36 cars 150 m downstream, plus the Kawayu public car park. Steps lead straight down from the inn street to the riverbank
- Phone
- 0735-42-0735
- Official site
- hongu.jp ↗
- Open in Google Maps
- Google Maps ↗
Essentials
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Why go
- Dec–Feb only: a river dammed into a bath
- Free, swimwear required
- Dig your own pool in summer
A winter miracle: the river itself becomes a hot bath
Kawayu Onsen's Sennin-buro is a giant outdoor bath that appears only from December to February on the bed of the Otou river, ten minutes by car from Kumano Hongu Taisha in Hongu, Tanabe, Wakayama. Kawayu sits on rare ground where 73°C water wells up wherever you dig the riverbed; in summer the tradition is to dig your own private bath with a shovel, but in winter, when the river runs low and cold, the local tourist association excavates the riverbed with heavy machinery and builds a stone dam to create a mixed open-air bath 15 metres wide and 50 metres long, named for the 'thousand people' (sennin) it supposedly holds. Spring water rising from the riverbed blends with the current to around 40°C; bathing is free and in swimwear. It is open from 6:30 in the morning until 10 at night, and every Saturday evening the 'Yukemuri Toro' lights hundreds of lanterns along the bank — steam rising between the mountains under the stars and lantern-light is an emblem of a Kumano winter. The 2025–26 season runs from 1 December to 28 February 2026; it closes on days when rain swells the river, so check with the tourist association that morning. Remember that from March to November the Sennin-buro simply does not exist.
Into the river in swimwear — hunting the hot spots with your feet
From the inn street in Kawayu, stone steps lead down to the riverbank where a broad pool enclosed by the dam sends up steam. You change into swimwear in simple changing tents (separate for men and women) on the bank, but with the winter air so cold it is wiser to put your swimsuit on at your inn and come down in a yukata or coat; bring sandals, a big towel and a plastic bag. Inside, the bottom is sand and gravel and the water knee- to waist-deep; where the source rises it is hot enough to warm the soles of your feet, while by the dam where the river enters it is tepid, and the fun is in roaming to find the spot that suits you — dig a little into the gravel and hotter water seeps up. As mixed bathing in swimwear it is easy for families, couples and foreign visitors, and children treat it as a natural pool. The loveliest moments are the misty early morning and the 'Yukemuri Toro' from 20:00 to 22:00 on Saturday nights, with a sky full of stars when clear. Soap and shampoo are of course forbidden, and since you chill fast on getting out, head straight to your inn's indoor bath or the Kawayu public bath (around ¥250) to warm up again. The day after rain the swollen river can submerge the dam or cool the water and the bath may be suspended, so leave slack in your plans.
Season and weather checks, and the three baths of Hongu
The Sennin-buro runs every year from 1 December to 28 February (the same for the 2025–26 season), 6:30–22:00, free of charge. In early December the start may slip depending on river levels, and even in season it is suspended after heavy rain, so check the day's status with the Kumano Hongu Tourist Association (0735-42-0735) or its official social media. If you visit between March and November there is no Sennin-buro; instead borrow a shovel from your inn to dig a 'home-made' bath in the riverbed, or use the Kawayu public bath and the inns' day bathing. A recommended two-day plan: day one, Kumano Hayatama Taisha and Kamikura Shrine in Shingu, bus to Hongu, worship at Oyunohara and Hongu Taisha, overnight in Kawayu and a lantern-lit soak in the Sennin-buro after dinner (the Yukemuri Toro if it is Saturday); day two, the bath again in the morning mist, Tsuboyu at Yunomine, then the great rotenburo at Watarase or a walk on the Kumano Kodo to complete the 'three baths of Hongu'. Winter days in Kumano can hover near freezing even at noon, so dress warmly — but the thicker steam makes the best photographs, and with few tourists it is wonderfully quiet. Kawayu's inns are small and fill early at weekends and New Year, so book ahead.
Before you go
- No official tattoo policy is published — ask at reception.
- Open seasonally only — check the official site for operating dates before you go.
- Last entry is 30–60 minutes before closing.
Features
Mood & scenery
Rules & private
Who with
Convenience
Amenities
✔ Verified operating: 2026-09 Operating status and rates cross-checked against the official site and onsen guides (full source notes in Japanese on the JA page)
Prices and hours change. Check official sources before visiting.
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