Gunma

The largest resort here discharges an extraordinary volume of water and it comes out of the ground at a temperature nobody could enter. Rather than dilute it, which would weaken the minerals people come for, the town runs it through long open wooden channels in the middle of the square so that it loses heat on the way to the bathhouses. The apparatus is the centre of the town and it steams day and night.

The associated practice of stirring the water with long paddles, once simply the work of cooling it further before a bath, survives as a demonstration with singing. Go in the evening when the steam catches the lights, walk the channels from the top end down, and take the free footbaths along the street. This is also the reason the water here feels sharper than at gentler resorts — it is strongly acidic, so keep it out of your eyes and rinse silver jewellery afterwards.

Two nights, because this is a prefecture you sleep in rather than see. The whole logic of Gunma is hot-spring towns, and a day trip to one is a compromise: the reason to go to Kusatsu or Ikaho is the evening, the second bath, and the street in the dark.

The routes are radial rather than circular, which surprises people. From Takasaki, Kusatsu is about two and a half hours by train and bus; Ikaho is roughly ninety minutes; Minakami is about an hour and a quarter north on the line toward Niigata. They do not usefully connect to each other — going from Kusatsu to Minakami means coming back down the mountain first.

So the shape is: pick one hot-spring town, stay two nights, and use the second day for what is around it. Three or four days lets you do two towns with a return through Takasaki in between, which is less annoying than it sounds because the shinkansen makes Takasaki fifty minutes from Tokyo.

Trains and buses reach the famous towns and nothing between them. Kusatsu, Ikaho and Minakami all have a rail-plus-bus route from Takasaki that works, is well signposted and is used by domestic visitors constantly; if your trip is one town, you do not need a car.

A car is what lets you treat Gunma as a region rather than a destination — the Oze marshes, the Tone valley, the mountain roads over to Nikko and Niigata, the smaller baths that never got a bus. It also solves the awkwardness of the radial layout. Winter complicates it: this is snow country on the northern side, several passes close, and the road up to Kusatsu is cleared but demands proper tyres.

The Joetsu and Hokuriku Shinkansen both cross the prefecture, putting Takasaki about 50 minutes from Tokyo — one of the shortest shinkansen hops in the country. From there the JR Agatsuma line runs to Naganohara-Kusatsuguchi, where a 25-minute bus finishes the trip to Kusatsu; direct limited express services also run from Ueno. Ikaho and the Tomioka mill are reachable by bus and local train from Takasaki. Beyond that, the mountain roads matter more than the rails: Oze, Akagi and the Nikko-Gunma border need a car or a seasonal bus, and several passes close under snow from November into spring.

The plain in the south of this prefecture grew a great deal of wheat, and the local food reflects that far more than rice does. One of the country's three most-named udon comes from the approach road to a temple in the hills and is served cold with a dipping sauce. Fist-sized steamed buns, skewered and painted with sweet miso, are sold at roadside stands and festivals across the plain. Devil's tongue root, processed into a firm jelly, turns up in hotpots, on skewers and as a snack.

That gives the prefecture a distinctive everyday menu that has nothing to do with hot springs, and it is worth eating deliberately rather than defaulting to the inn's set dinner every night. The buns in particular are a street food rather than a restaurant dish and are best bought from a stall in the open air.

The New Year holiday and the weekends of peak autumn colour, when the hot-spring towns fill with domestic visitors and rooms are both scarce and expensive. Gunma is Tokyo's bath, and it books like it.

The genuinely poor window is late March into April at altitude. The ski season has ended, the marshes and mountain roads have not opened — Oze in particular does not really begin until late May — and the towns are between seasons. Down in the plain around Takasaki it is fine, but nobody comes to Gunma for the plain. Note also that Kusatsu sits high enough to be cold well into spring, which catches visitors who packed for the Kanto weather they left behind.

The onsen towns are winter destinations and Kusatsu at 1,200 metres gets real snow from December to March, with ski runs above the town. The plain below is the opposite: Maebashi and Tatebayashi are among the hottest places in Japan in August, regularly above 35°C, and the dry winter wind keeps the lowlands clear and snow-free. Oze's marshland boardwalks open from late May, with cotton grass in June and alpine colour in early October. Mt. Haruna and Mt. Akagi are best from May to November. Late October is when the mountain foliage and the still-warm baths overlap.

Gunma grows a great deal of wheat, which is why the local staples are flour rather than rice. Mizusawa udon, made along the approach to Mizusawa temple in Ikaho, is one of the three named udon of Japan and is served cold with dipping sauce. Yakimanju are fist-sized steamed buns skewered and painted with sweet miso, sold at festivals and roadside stands across the plain. Shimonita in the southwest grows a thick, short negi eaten cooked rather than raw. Konnyaku, made from local devil's tongue root, appears in almost everything.

A first visit is Kusatsu, two nights, in any season but preferably a cold one. The town is built around a field of steaming water in the middle of it, the smell of sulphur is everywhere, the bathing is unusually hot and unusually good, and there is a public performance of the traditional water-cooling routine that is more interesting than it sounds. It requires no car and very little planning.

A second visit should be Minakami or the Oze marshes and should involve walking. Northern Gunma is a mountain landscape with rafting, gorges and one of the great high moorland boardwalks in the country, and it is the version of the prefecture that has nothing to do with soaking. Late spring and autumn are the windows; a car turns it from a couple of fixed points into a proper region.