The hook
A city that steams. Beppu sits on more hot-spring water than anywhere else in Japan, and on a cold morning the vapour rises out of drains, gutters and hillsides all over town — with the ghibli-looking village of Yufuin twenty minutes inland.
01Why it's worth it
Beppu produces a greater volume of geothermal water than any other place in Japan, and more than almost anywhere on earth. The practical consequence is that the town is not built around an onsen; it is built on top of them. Steam vents through street grates. Neighbourhood bathhouses cost a couple of hundred yen and are used by people on the way home from work.
The jigoku — the "hells" — are the tourist face of it: pools too hot to enter, one cobalt blue, one blood red, kept as a viewing circuit. Worth an afternoon, and not the reason to come.
The reason to come is the ordinary bathing. Sand baths where you are buried in volcanically heated sand on the beach, steam baths, and the small municipal sento scattered through the back streets.
Yufuin, inland under Mount Yufu, is the soft counterpart — a walkable village of craft shops, a lake and high-end ryokan, and the single best description of it in the corpus is a Kyushu resident's: "it's like this little floral town that looks like it came out of a ghibli movie."
Wider Oita and the Kumamoto border hold Kurokawa Onsen, a village of riverside baths that is deliberately kept low-rise and is the connoisseur's pick.
02How to experience it
Train from Fukuoka, about two hours. Give it two or three days: Beppu for the municipal baths and the sand bath, Yufuin as a day or an overnight, Kurokawa if you have a car. Stay in a ryokan at least one night — this is the region where that is the point rather than the splurge. Winter is best: the colder the air, the more visible the steam.
The honest note
Learn onsen etiquette before you arrive, because the older baths assume you know it. A first-timer's account of Beppu is the useful warning: "at some public onsen (like the first two onsen I ever visited, in Beppu!) there are no showers and no toiletries provided. I had to work out that you crouched by the bath and washed yourself by scooping bowls full of water out of the bath and pouring them over yourself repeatedly. I had brought my own toiletries in case they weren't provided, which was lucky." Wash thoroughly before entering, bring your own soap, and treat the small municipal baths as neighbourhood facilities rather than attractions.
Do not bring a camera into a bath. This should not need saying and evidently does — a Japan resident on tourists in Beppu: "there was a young european dude taking photos with a SLR he had hidden under a towel."
Tattoos are a real obstacle at many traditional baths in Japan. Check individual bathhouses in advance or book a room with a private bath.
It is off the main route, and that is the trade. Beppu is not a stop between Tokyo and Kyoto; it is a separate trip into Kyushu. The recommendation that puts it best treats it as a base decision rather than a detour: "If you really want off the beaten bath, go base yourself out of Fukuoka… Hit up Kurokawa onsen, Yufuin, or Beppu. Tons of Ryokans in the area and way less tourists. Rent a car and be free."
Yufuin is the busy one. It is small, pretty and heavily day-tripped; the main street can be shoulder to shoulder. Stay the night and you get it before and after the coaches.
Beppu town itself is not beautiful. It is a slightly faded mid-century resort city. The steam, the baths and the setting are the appeal — not the architecture.
From the locals
The most complete account comes from someone who lives in Kyushu, answering what the most off-the-beaten-path part of Japan is: "Oita is one of the most beautiful places in Japan in my opinion. My friend took me on a random trip one time and didn't say where we were going. Stopped off in a little town called Yufuin, it's like this little floral town that looks like it came out of a ghibli movie. Then we went further into Beppu. We basically drove around and found hot springs and things to see. Smoke was filling into the sky, and I remember eating eggs that were steamed from one of the natural hot springs. TLDR: Oita is beautiful, strongly recommend."
Asked for the best thermal baths they had ever been to — a question with the whole world available — one answer named this town and did not qualify it: "Beppu, Japan. Stayed at a private onsen. I felt like I was literally in heaven."
And from someone visiting family rather than sightseeing, which is usually the more reliable witness: "I visited my relatives in Beppu this January, their onsens are amazing and the small city is filled with great food and amazing scenery."