What Is an Onsen Hotel? How to Use an Onsen

Japan's Hot Springs Act sets the line precisely. Water counts as onsen if it emerges from the ground at twenty five degrees Celsius or warmer, or, failing that temperature, if it carries a specified concentration of one of nineteen designated minerals, sulphur and iron among them. A sento has no such requirement and no interest in claiming one; it heats ordinary water for residents without a bath of their own at home, a use that has thinned over the decades without disappearing.

A ryokan's private tub sits between the two. Some are supplied from a licensed spring by pipe or by tanker and are onsen in every legal sense; others are simply well-made baths filled with heated water, and the difference is disclosed rather than obvious from looking at it. The private tub in a Kyoto ryokan room, and how that provenance is actually checked, is its own subject, told in full in The Room with Its Own Onsen: Kyoto. What follows here is simpler: what happens once a guest is standing in front of any of the three, spring-fed or not.

An indoor onsen and an outdoor one, a rotenburo, are often drawn from the same source inside a single building, and the choice between them is a choice of temperature and air rather than of water. The indoor pool keeps its heat more evenly and suits a short, deliberate soak. The outdoor one loses warmth to the air faster, which is exactly why a cold morning or a light snowfall is when it earns its reputation, the shoulders warm and the face cold at the same time.

The sequence barely varies between a mountain ryokan and a city sento, and once learned it asks nothing further of a guest, ever again.

• Shoes come off at the entrance, left in a locker or on a low shelf, and go no further than that point.
• In the changing room, belongings are folded into a basket or locker, and only the small hand towel goes on into the onsen.
• The towel is folded on the head or set on the stone edge, but it never goes into the water.
• Long hair is tied up, kept clear of the water entirely.
• Before the onsen is entered, a guest washes sitting at one of the low stations along the wall, soap and shampoo rinsed off completely, then pours a few scoops of the spring water over the shoulders, the kakeyu, to meet its heat before stepping in.
• Entry is slow, feet first rather than a straight step down; the water often runs above forty degrees Celsius, and it rewards patience.
• Ten to twenty minutes is a good soak, longer only once acclimatised. Swimming, diving and vigorous movement have no place here, and neither does a phone, anywhere near the water.
• A cold plunge or a sauna, where the building has one, follows the hot spring rather than replacing it; the two alternate rather than compete.
• Before returning to the changing room, a guest dries off at the edge with the small towel, so the floor beyond stays dry, and the minerals of the spring are left to do their work rather than rinsed away.

Getting dressed again, in a ryokan, usually means a yukata rather than the clothes left behind that morning. It closes left side over right, the same direction as a kimono; right over left is kept for dressing the dead, and Japanese staff notice the reversal instantly even when a guest does not. The sash sits at the natural waist in a simple bow rather than a formal knot, and the whole garment is built to move rather than to be arranged once and left alone.

Many shared onsen still ask guests with tattoos not to enter, though a growing number of properties, particularly in resort towns, now welcome them, and the Japan Tourism Agency has encouraged the rest to reconsider. A private onsen removes the question entirely.

The onsen itself is a quiet place. Voices stay low, there is no splashing or swimming, and a guest slips in gently and leaves room for others. It is the stillness, shared with strangers or with no one at all, that makes the water restful.

For guests who would rather keep the water to themselves, a suite with its own onsen is the answer, theirs at any hour, its water drawn from the same spring as the ryokan's great pools.

A cup of water before and after the soak is the custom, and a shorter soak suits the hottest springs.

The signage rewards a small vocabulary rather than fluency. 湯, painted alone in red over a doorway or curtain, means hot water and is the oldest, plainest sign an onsen has. 露天風呂 names an open-air onsen, usually the one worth stepping outside for. 貸切 marks an onsen reserved for one party at a time, the private option that answers most of the questions above simply by removing them.

No two springs are the same, and the Japanese read them the way a wine drinker reads a slope. Sulphur springs, the commonest in the volcanic mountains, smell faintly of struck matches and turn milky in the pool; the old wooden inns of Nyuto in Akita are known for water the colour of skimmed milk. Salt springs keep their heat on the skin long after the soak and suit a cold night. Iron springs come out of the ground clear and turn red-brown as they meet the air.

Arima Onsen, in the hills behind Kobe, has both kinds at once and names them after metals: Kinsen, the gold water, rich in iron and salt and rust-red in the pool, and Ginsen, the silver water, clear and carbonated. At Nyuto, one ryokan keeps a Gold spring and a Silver spring of its own, the one cloudy and the other clear, flowing into eight onsen beside a mountain stream. In Hokkaidō, a ryokan at Noboribetsu draws on four kinds of spring water from the steaming crater of Jigokudani above the town.

A ryokan with two springs of its own, Nyuto Onsen →

A ryokan on four springs, Noboribetsu →

Kusatsu, in the mountains of Gunma, has the largest natural flow of any onsen town in Japan, and its centre is the Yubatake, a field of steaming water running down wooden channels in the square, acid and sulphurous and pale green in the boxes. Beppu, on the coast of Kyushu, has more sources and more water than anywhere else in the country, and its steam rises from the streets themselves.

Kinosaki Onsen, near the Sea of Japan in Hyogo, is the town of willows and stone bridges where guests walk the canal in yukata and wooden geta from one of its seven public bathhouses to the next, and its most celebrated ryokan keeps its own onsen on the town's springs. Ginzan Onsen, in the mountains of Yamagata, is a single street of tall wooden inns facing each other across a narrow river, gas-lit at dusk, and the most remarkable of them keeps eight rooms behind a Taisho-era facade. At Yamashiro Onsen in Kaga, one ryokan has kept its three bathhouses on its own spring, in the same family, since 1639.

Kinosaki Onsen →

Kinosaki's most celebrated ryokan →

Ginzan Onsen →

A ryokan kept by one family since 1639, Yamashiro Onsen →

Kusatsu Onsen →

It all comes together in a ryokan, where the onsen is a rhythm repeated through a single stay. It is taken before dinner, while the kitchen still has an hour of work ahead of it, to settle a day of walking into something ready to sit still. It is taken again at night, later than seems reasonable, once the corridor has gone quiet and the water has had the whole evening to keep its heat. And it is taken once more before breakfast, when the light through the steam is the only remarkable thing left to notice before the day properly starts. Between the three, the garden beyond the glass keeps changing, evening to full dark to first light, without the guest ever having to leave the building to notice it.

An onsen taken three times in one stay stops being a task and becomes the shape of the day itself.

A guest who has washed correctly, entered slowly, and returned to the same water at three different hours of one day has let the water set the pace of the stay, which no single visit to a bathhouse can offer.

Read The Room with Its Own Onsen: Kyoto →

More of the Japan Edition on ryokan and onsen →

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