Oita Prefecture occupies the northeastern corner of Kyushu and is Japan's hot spring capital. Beppu, on the coast, produces more hot spring water than anywhere else in the country — steam rises from drains, hillsides, and hotel lobbies. The "hells" (jigoku) are boiling pools of vivid blue, red, and grey that you look at rather than bathe in, but the city has hundreds of public baths where you can soak for a few hundred yen.
Inland, the onsen town of Yufuin is quieter and more refined — a single main street lined with small galleries and cafes, with views of the twin-peaked Mount Yufu. The Kunisaki Peninsula in the north has stone Buddhas carved into cliff faces, remote temples reached by forest paths, and very few tourists.
Oita city itself is a pleasant, mid-sized Japanese city with good food — the local speciality is toriten (chicken tempura) and kabosu citrus flavours everything from sashimi to shochu. The reconstructed grounds of Funai Castle, Shigeru Ban's striking prefectural art museum, and the rooftop garden above Oita Station are all within easy walking distance of each other. It is a practical base, well connected by train to Fukuoka and the rest of Kyushu.