Beppu has been a hot spring resort town since at least the 8th century — Buddhist monk Gyōki is credited in local legend with discovering its waters. Its modern incarnation as a mass-tourism destination was largely shaped by one man: Aburaya Kumahachi, an early 20th-century entrepreneur who built roads, piers, and tourist infrastructure entirely at his own expense to promote the city. He is considered the father of modern Beppu tourism. By the 1920s Beppu had become Japan's most visited domestic resort, drawing millions annually. The city still receives around 10 million visitors per year — extraordinary for a population of 117,000. Fun facts: there are more ryokan per square kilometre in Beppu than anywhere in Japan; the city has eight distinct onsen districts (the "Beppu Hattō"), each with slightly different water chemistry; it sits on the Beppu-Shimabara graben — a fault zone running across northern Kyushu that continues to produce volcanic activity today.

Beppu is the second most geothermally active place on earth after Yellowstone — it releases more geothermal steam and hot water than anywhere else in Japan. The city has over 2,000 hot spring sources and more than 100 million litres of hot water flowing daily. You can see it from the moment you arrive: steam rising from gutters, from behind buildings, from between buildings, from the earth itself. It creates a visual atmosphere unlike anywhere else in the country — a city perpetually half-obscured by its own geology.

Why Beppu's onsen water is different: Most famous Japanese onsen (Hakone, Arima, Kusatsu) are fed by single mineral types — sulphur, sodium chloride, or iron. Beppu is unusual in having ten recognised spring types across its eight districts, including simple thermal, sodium bicarbonate, sulphur, iron, saline, and radioactive radium springs — each with different temperatures, colours, and therapeutic properties. The Kannawa district (where the Hells are) runs primarily on sulphate and chloride waters at 98–100°C, far hotter than the bathing springs. The Hamawaki district near the coast has milder, sodium-rich waters suited for soaking. This geological diversity — multiple spring chemistries within a single city — is what makes Beppu categorically different from anywhere else in Japan, and why serious onsen travellers consider it the benchmark.

Toriten (鶏天) is Oita Prefecture's most important food: chicken pieces dipped in a light tempura batter and fried, served with a ponzu-mustard dipping sauce. It was developed in Beppu in the 1940s as a way to serve protein efficiently to the city's onsen visitors. The key is the batter — lighter and crispier than standard tempura, applied thinly so the chicken flavour is primary. The quality of the chicken matters enormously: Oita's Bungo dori (local free-range chicken) has a dense, flavourful flesh that makes the dish. Order it at Toyotsune before the Hells visit; it's the correct order of operations.

The "Nine Hells of Beppu" are a series of natural hot spring pools, each with a different character: Umi Jigoku (cobalt blue, 98°C), Chinoike Jigoku (blood-red from iron oxide), Tatsumaki Jigoku (a geyser that erupts every 30–40 minutes). They were named "hells" because the temperatures make them unusable for bathing — they're sources of geothermal energy rather than relaxation. The most interesting is Shiraike Jigoku (White Pond Hell) — a milky white pool with large carp swimming below the surface in the 40°C water at the edges. The Jigoku Mushi Pudding (steamed in geothermal steam) sold at Umi Jigoku is worth the ¥300 — a surprisingly serious product.

Hoshino Resorts' KAI brand positions its hotels around a specific regional story — in Beppu's case, the onsen culture and the architecture of steam. The dinner tonight is booked at 5:30pm (you have a confirmed reservation); the kaiseki menu will use local Oita ingredients throughout. Sekiaji (horse mackerel from Oita coastal waters), Bungo beef, and the spring vegetables of Kyushu will all appear. This is the right way to start the group leg — a structured, unhurried dinner that sets the register for 6 days together.