Zaō Onsen — photo: 663highland · CC BY-SA 4.0 · Wikimedia Commons
Outdoor onsen in Japan: what a rotenburo is, the big public ones, and bathing in snow
An outdoor onsen bath is called a 露天風呂 (rotenburo): a pool of hot spring water under the open sky, usually built of stone or wood, sometimes with a roof over part of it and a fence around it. Most inns and day baths that have one also have an indoor bath, and the two work as a pair. This guide covers how that pair works, the different kinds of outdoor bath you can actually visit, what changes when it is cold or snowing, and the Japanese words that tell you whether a place has one.
What a rotenburo is, and how it fits with the indoor bath
The indoor bath is the 内湯 (uchiyu). At a normal inn or day bath you undress in the changing room, walk into the indoor bath, wash at the taps there, and then go out through a door to the outdoor bath. The washing always happens indoors. An outdoor bath rarely has taps of its own, and the rule about washing before you get in applies to it exactly as it does inside. See onsen etiquette for the order.
The water is usually the same spring, piped to both pools. Because the outdoor pool loses heat to the air, it is often a little cooler than the indoor one in winter. The other rules do not change outside: no swimsuit, the small towel stays out of the water, no photos.
Three things are different in practice:
- It may be on the other side today. Many inns have one outdoor bath that is better than the other and swap the men's and women's sides once a day so both get a turn. The sign is 入れ替え (irekae), with the time. If you came for a particular outdoor bath, read the board at the entrance. More on the signs in are onsen mixed gender?
- It has opening hours. Outdoor baths are often closed late at night, for cleaning in the morning, and in storms or heavy snow, even when the indoor bath stays open.
- Things fall into it. Leaves, insects, snow, rain. That is part of it. Staff clean the pool; you do not need to fish things out.
The kinds of outdoor bath you can visit
"Outdoor onsen" covers several quite different things. Which one you mean decides where you go.
Large public outdoor pools
A few towns have a big outdoor bath run as its own facility, which anyone can walk into for a fee. The best known is 西の河原露天風呂 (Sainokawara rotenburo) in Kusatsu, at the top of a park above the town. The national tourism agency's guide gives it about 500 square metres and room for around a hundred people, with a men's side and a women's side. Its published hours are 7:00 to 20:00 from April to November and 9:00 to 20:00 from December to March, with last entry at 19:30; the fee has changed more than once, so check it on the day. The water is Kusatsu's: acidic, with sulfur, between 44.9 and 94.5 °C at the sources in our records, and pH 1.0 to 2.2. It stings small cuts.
The other famous one is the big outdoor bath at Zao in Yamagata, a series of pools in a stream valley below the ski slopes. It is closed in winter. It usually opens from mid or late April to mid or late November, depending on snow, which means it is shut during the ski season when most visitors come. Zao's small public baths in the town are open all year.
A river that becomes a bath
At Kawayu Onsen in Wakayama, hot water comes up through the gravel of the river bed. Every winter part of the Oto river is dammed off to make a large pool in the river itself, called the 仙人風呂 (sennin-buro). It is usually open from 1 December to the end of February, and on some days it cannot be used because the river is too high or the water too cool. Our records give the source at 73 °C, alkaline, with chloride and bicarbonate water. It is free, in the open beside the road, and mixed, and people bathe there in swimsuits or bath wraps, which is the one kind of outdoor bath where that is normal. It is about 2.4 km in a straight line from Yunomine, so the two are easy to combine on the Kumano pilgrimage roads.
Bath-hopping between inns
In Kurokawa in Kumamoto, almost every inn has an outdoor bath by the river or in the woods, and a wooden pass lets day visitors use three of them. This is the place where outdoor baths are the point of the town rather than an extra. The baths belong to the inns, so each has its own hours and some are closed to day visitors on some days. See onsen hopping for the other towns built around more than one bath.
Mixed outdoor baths with bath wear
A few old inns keep a large outdoor bath that men and women share. At Takaragawa Onsen in Gunma, a well-known one with several pools along a river, both men and women wear a rented bath wrap in the mixed outdoor baths, and there is a separate outdoor bath for women only. This is the exception: almost everywhere else the outdoor bath is split like the indoor one. See are onsen mixed gender?
Your own outdoor bath
The quietest version is the one you do not share: a private outdoor bath you book by the hour, or a room with its own tub on the balcony, 露天風呂付き客室 (rotenburo-tsuki kyakushitsu). See private onsen baths.
Bathing outside in snow
Sitting in hot water while snow falls has its own word, 雪見風呂 (yukimi-buro), "snow-viewing bath", and it is the reason many people want an outdoor bath at all. It is easy to get, because a large share of Japan's hot springs are in the snowy north and in the mountains; see where Japan's hot springs are. Towns with a guide on this site that sit under snow for much of the winter include Nyuto, Ginzan, Shirahone and Noboribetsu; ask the inn whether its outdoor bath stays open in winter. For the months, see when to go.
What is different in the cold:
- The walk from the indoor bath to the outdoor one is short but freezing. Wet stone and wooden decks ice over. Walk, do not hurry, and use the handrail if there is one.
- Your head is out in the air while your body is in hot water. Folding the small towel on your head is the usual answer, and it keeps wet hair from freezing.
- Because the air is cold, it is easy to stay in much longer than you meant. Keep each soak short, go back inside to warm up, and drink water between baths. See how hot onsen water is.
- In heavy snow or wind, an inn may close its outdoor bath for the night. That is a safety call, not a service failure.
How to tell if a place has one
The words to look for on an inn's website, a booking page or the sign at a day bath:
- 露天風呂 (rotenburo): outdoor bath. Often shortened to 露天.
- 大露天風呂 (dai-rotenburo): a large outdoor bath.
- 混浴露天風呂: a mixed outdoor bath.
- 貸切露天風呂 (kashikiri rotenburo): a private outdoor bath you book.
- 露天風呂付き客室: a room with its own outdoor tub.
- 内湯のみ (uchiyu nomi): indoor bath only.
Our records, which come from public sources about hot spring places rather than from inns, do not say which places have an outdoor bath, so the town pages on this site cannot answer that question. The inn's own bath page, usually with photos, can. City day baths and neighbourhood sento often have no outdoor bath at all, or a small courtyard pool; resort towns and mountain inns usually do. See the 露天風呂 entry in onsen in Japanese for the other words on the signs.
A few practical points
- Wash indoors first, every time, even if you only came for the outdoor bath.
- Do not take your phone out to the outdoor bath. Other guests are a few metres away, and many baths ban phones beyond the changing room.
- Seasonal baths, like Zao's big pool and the river bath at Kawayu, open and close by the year's weather. Check the dates for the year you go.
- Tattoo rules are the same outside as inside. See going to an onsen with tattoos.
New to this? Start with how an onsen stay actually works and onsen etiquette. Want an outdoor bath to yourself? See private onsen baths. Going for snow? See when to go.