Kumamoto

Aso is not a mountain you look at from a viewpoint. The caldera is roughly the size of a small city district, and the floor of it holds farms, schools, rice fields, hot springs and a railway line, with the central cones rising out of the middle and the old crater wall standing around the whole thing like a horizon that does not move. The scale only registers once you are inside and realise the ridge on every side is the same ridge.

That geography is why the prefecture rewards a car and punishes a tight schedule. The rim roads look short on a map and are slow in practice, weather on the tops is often completely different from the weather on the floor, and the most memorable stretches are the ones between the places with names. Access to the active crater itself is governed by gas readings and can close with no notice at all, so treat standing on the rim as a bonus rather than the reason you drove up.

Three days. The city and its castle are one — the castle is one of the great fortifications in Japan and has been under reconstruction since the 2016 earthquake, with the keep reopened and parts of the grounds still being rebuilt, which is itself worth seeing.

Day two is Aso: the largest caldera in Japan with a live volcano in the middle of it and a working farming landscape inside the crater walls. It is about ninety minutes east of the city and access to the crater rim depends on the volcanic alert level, which changes.

Day three goes to Kurokawa Onsen, a hot-spring village of two dozen inns in a wooded gorge with an open-air-bath pass that lets you use three of them, roughly two hours from the city. Or south to Hitoyoshi and the river.

Four days does all three without hurrying, and that is the trip Kumamoto deserves.

Two large earthquakes struck the prefecture in April 2016. The damage was concentrated on the castle and on the roads and rail linking the city to Aso, and repair on that scale is measured in decades rather than seasons. The castle keep has reopened and there is a raised walkway that lets visitors in over the works, but large sections of stone wall are still dismantled, numbered and waiting, and you will see as much scaffolding as masonry.

This is worth knowing in advance because it changes what the visit is. Arriving expecting an intact fortress is a letdown; arriving to watch one of the largest stone-wall restorations in the country in progress is genuinely interesting, and the site explains itself well. On the Aso side, road and rail routes that were severed have since reopened, but services are lighter than the timetable history suggests, so confirm connections rather than assuming the map is current.

The Kyushu Shinkansen puts Kumamoto about 35 minutes from Hakata and an hour from Kagoshima-Chuo. Kumamoto Airport sits on the way to Aso. The city has trams to the castle and the centre. Aso is the complication: the JR Hoshu line was cut by the 2016 earthquakes and has since reopened, but services are limited, and reaching the crater involves a bus and, when it is running, a shuttle from Aso Station. Kurokawa Onsen has no railway and is served by highway bus from Fukuoka and Kumamoto or reached by car. For the caldera rim roads and the Amakusa islands, drive.

A car for Aso and Kurokawa, trains for the city and the south. Kumamoto City has a tram and the castle is central; the shinkansen runs down the western side of the prefecture toward Kagoshima.

The interior is different. The Aso caldera has a rail line across it and buses to the crater, but the farms, the viewpoints and the grasslands are a driving landscape, and Kurokawa has no station at all — it is a bus from Aso or a drive. Given that the interior is the reason to come, hire a car. Check volcanic alert status before planning the crater rim, since access closes at short notice and has done for extended periods.

Aso in poor visibility, which is a real risk rather than bad luck — the caldera generates its own weather and the crater is frequently in cloud. Spring and autumn are more reliable than summer.

The rainy season in June brings genuinely heavy rain to central Kyushu with landslides and road closures in the mountains; this is the region where that is a practical constraint rather than an inconvenience. Late summer typhoons do the same. Winter is cold in the caldera and at Kurokawa, which is exactly when the outdoor baths in the gorge are at their best.

The caldera and the highlands are cooler than the city and are best from April to November; the Aso grasslands are burned off in late winter and green up from March. Access to the crater rim depends on volcanic activity and gas levels and is closed without notice, so check on the day rather than assuming. Kumamoto City is hot in summer above 34°C and mild in winter with January highs near 11°C, while Kurokawa and the Kuju highlands see snow. The June rainy season is heavy in the mountains and has caused landslides. Autumn colour reaches Kurokawa in early November.

Basashi, raw horse, is eaten here more than anywhere else in Japan, sliced thin with ginger and garlic and often with a fatty cut alongside — Kumamoto has bred horses for it for centuries. Karashi renkon is lotus root packed with mustard miso, battered and fried, invented to fortify a sickly daimyo. Kumamoto ramen sits between Hakata and Kagoshima styles, with pork broth, thicker noodles and burnt garlic oil. The Aso highlands raise akaushi, a red-haired beef breed, and the caldera's dairy farms sell milk and soft-serve at the roadside.

A first visit is the castle and Aso. The castle's massive curved stone walls and its ongoing reconstruction make it a more interesting site now than it was before the earthquake, because you can see how it was built. Aso is genuinely hard to grasp until you are inside it — a crater twenty-five kilometres across with towns, farms and railways in it, and a smoking cone in the middle.

A second visit is Kurokawa Onsen and the southern rivers. Kurokawa did something unusual: the inns agreed to keep the village low-rise and wooden, banned neon, and sell a pass that lets day visitors bathe at three of them, which turns the whole village into one hot spring. Add the boat down the Kuma river at Hitoyoshi and you have a completely different prefecture from the volcanic one.