- Oka Castle Guide: The Impregnable Hilltop Fortress That Inspired "Kojo no Tsuki"
- Discover Oka Castle in Oita, a clifftop fortress famed for inspiring "Kojo no Tsuki." Walk along unfenced stone walls with panoramic views of the Kuju Mountains.
This guide introduces Oniishi Bouzu Jigoku, one of the seven hells on the Beppu Hell Tour.
Oniishi Bouzu Jigoku
Oniishi Bouzu Jigoku is one of the seven hells on the Beppu Hell Tour in Beppu City, Oita Prefecture. This hell features a boiling mud pool where hot mud bubbles up continuously through clay, and Oni no Takaibiki, a geyser that shoots powerful steam jets.
| Item | Details |
|---|---|
| Spring Type | Sodium Chloride Spring |
| Temperature | Approx. 99°C |
| Hours | 8:00 am–5:00 pm |
| Closed | Open year - round |
| Admission | Adults (high school and above): ¥500 / Children (elementary/junior high): ¥250 |
| Smoking | No smoking area |
| Access (Car) | Approx. 5 min (2 km) from Beppu IC on Oita Expressway |
| Access (Bus) | 20 min by Kamenoi Bus bound for Kannawa from JR Beppu Station West Exit, 1 min walk from Umi Jigoku - mae stop |
| Address | 559 - 1 Kannawa, Beppu City, Oita 874 - 0045 |
| Official Site | https://oniishi.com/oniishi-bouzu-jigoku/ |
Oniishi Bouzu Jigoku is located in the southern part of the seven Beppu Hells. Umi Jigoku is right next door, and Kamado Jigoku is about a 5-minute walk away.
A Monochrome World Unlike Any Other Hell
The distinctive feature of Oniishi Bouzu Jigoku is the gray hot mud that bubbles up in spheres of various sizes. Because these bubbles resemble bald monk heads (bouzu in Japanese), combined with the local place name Oniishi, it came to be called Oniishi Bouzu Jigoku.
The hot mud at Oniishi Bouzu Jigoku forms when underground hot water erupts to the surface. This hot water is groundwater heated by underground magma and geothermal energy. The hot water here contains high concentrations of gases like hydrogen sulfide and methane.
The color of the boiling mud pool is a grayish white, similar to a mud bath. Seeing it up close, you will be amazed by its beauty.
The Powerful Geyser: Oni no Takaibiki
Oni no Takaibiki (Demon’s Loud Snoring) is a geyser. It erupts approximately every 10 minutes, shooting 100°C steam upward with a thunderous sound resembling a demon’s snore.
The steam bursting from between the rocks is quite powerful. When sunlight hits the rising steam, it creates a curtain of light, producing a magical scene.
Spacious Foot Bath for Relaxation
Oniishi Bouzu Jigoku also has a foot bath. Since it uses clear hot spring water rather than mud, you can easily enjoy it. Towels are not provided, so bring your own.
Oniishi Specialties: Hell-Steamed Pudding and Onsen Eggs
Oniishi Bouzu Jigoku has a shop called “Hitoyasumi Kobiri” that serves popular original menu items.
The most popular items are the “Hell-Steamed Pudding” and “Onsen Boiled Eggs.”
They also offer a variety of other treats like “Kanmuri-dori Manju” (steamed buns with local chicken), all cooked using the hell’s steam. Be sure to try them.
Journey to the Only Colorless World Among the Seven Hells
Gray hot mud bubbling in the boiling mud pool, 100°C steam roaring at Oni no Takaibiki.
Oniishi Bouzu Jigoku is the only achromatic world among the seven hells.
Oniishi Bouzu Jigoku has a long history, appearing in the “Bungo Fudoki” written in 733 CE. It was already a tourist attraction by the Meiji era.
In those days, the hot mud made rice cultivation impossible and the land uninhabitable—truly a hellish landscape. However, this natural phenomenon became a topic of fascination, and over many years, it transformed into a tourist destination.
Precisely because it is monochrome, the movement and texture of the hot mud stand out even more. Watch the mud swell, pop, and swell again—this mesmerizing cycle makes you lose track of time.
Visit in person to experience this unique landscape for yourself.
