Oniishibozu Jigoku (Monk's Head Hell)

Oniishibozu Jigoku takes its unusual name from the rhythmic bubbles of grey mud that swell and burst across its ponds, each rounded dome said to resemble the shaven head of a Buddhist monk - bozu being the Japanese word for a monk. Add the "oni" (demon) and "ishi" (stone) of the local place name and you get a hell that translates loosely as "demon-stone monk's-head hell," a mouthful that perfectly captures its slightly comic, slightly eerie character. It sits directly beside Umi Jigoku in the Kannawa district, so the two are almost always visited together.

The main attraction is the mud itself. Superheated water pushes thick grey clay upward in slow, deliberate blisters; each bubble domes to a smooth grey scalp before collapsing with a soft plop, only for another to rise beside it. Watching the ponds is oddly hypnotic - a natural, endlessly repeating rhythm driven by the same volcanic heat that powers all of Beppu's springs. Boardwalks and low fences let visitors get close to the action while keeping a safe distance from the scalding surface.

Unlike most of the seven hells, which are strictly for viewing, Oniishibozu also operates a genuine bathing facility called Oniishi no Yu, built beside the mud ponds. Here you can do what you cannot do in the hells themselves - actually soak in Beppu's famous water, in indoor and open-air baths fed by the same geothermal source. For travellers short on time who want both to see a hell and to experience a real onsen, this two-in-one arrangement is uniquely convenient.

The site is landscaped with tidy paths, seasonal plantings and a footbath, and shares in the collective national Place of Scenic Beauty designation that covers Beppu's hells. It tends to be quieter than the neighbouring Umi Jigoku, which absorbs most of the tour-bus crowds, so it can offer a more peaceful few minutes with the bubbling mud. Photographers enjoy the challenge of capturing a bubble at the instant it domes; a fast shutter and a little patience are rewarded.

Because it adjoins Umi Jigoku and is a short walk from Kamado, Oniyama and Shiraike, Oniishibozu fits naturally into the on-foot portion of the Beppu Jigoku Meguri. Many visitors spend only 20 to 25 minutes here before moving on, but those who add a soak at Oniishi no Yu can easily stay an hour or more.

Facilities include restrooms, a small shop and the bathhouse, and the flat boardwalks make the viewing area fairly accessible, with the baths requiring the usual steps and changing rooms of a Japanese onsen. As a study in the sheer variety of Beppu's geothermal expressions - here mud rather than the blue water of Umi or the red of Chinoike - Oniishibozu earns its place on the tour, and the chance to bathe on site makes it one of the more practical stops for anyone who came to Beppu to get in the water, not just gaze at it.