I used to think that only Mount Fuji was massive enough to have its own weather patterns, but 1,592-meter Mount Aso in Kyushu proved me wrong.

The clear skies and perfect late-September temperatures we were reveling in at the base of the hill dissipated quickly into mists and occasional thick cloud banks as we wound our way up the twisting western approach road to the summit of what is Japan’s largest active volcano.

Even when the skies cleared, it was to reveal a constantly smoking plume snaking up from the Nakadake crater, reminding us that — benign as our day’s adventure may seem — this towering mountain that dominates eastern Kumamoto Prefecture could erupt at any time.

It’s in large part due to Mount Aso that Kumamoto prefecture comes by its nickname of “fire country,” While most people think Mount Aso only comprises its cluster of five main peaks (known collectively as Aso-gotake), in truth those are all that remain of a truly massive volcano that blew its top a handful of times between 90,000 and 300,000 years ago.

The caldera (volcanic basin) that resulted from these cataclysmic events measures some 128 km in circumference, the largest of its kind in the world. Today, that caldera is a quiet and fertile place, boasting many farms and several towns, many of them known for their onsen (hot springs).

As the road crested the top of the central crater area, we were greeted with views of the Kusasenri Plateau. I was expecting a landscape akin to that of Mars, so this expansive grassy plain came as quite the shock. Late-season wildflowers were blooming on the hillocks, and in the distance a group on horseback rode at a peaceful plodding gait along a dirt track. If it weren’t for the wisps of smoke hanging over it all, you could almost forget there was a volcano just down the road.

Across the plateau, tour buses disgorged their passengers at the Aso Volcano Museum. With a yawningly large collection of rocks and limited English signage, it’s not a place all visitors will want to linger. Yet on days when access to the crater is barred for safety reasons, it’s the one place to get a bird’s-eye view of the seismic action.

Cameras installed around the rim of the Nakadake crater continuously broadcast a live feed to the museum’s massive video screens, giving visitors the only glimpse of the volcano they can get when the wind is blowing the wrong way and poison-gas restrictions are in place.

Thankfully, nothing was stopping us seeing the crater, and we made the final ascent up the toll road to its rim. There, finally, I beheld the lunaresque landscape I had been expecting, a barren wasteland of rocks and red dirt marred here and there by what looked like scorch marks. Despite the desertlike surroundings, the water roiling away inside the crater was an eye-popping turquoise akin to the ocean colors I’d enjoyed while living in Okinawa. This lake, however, is not one for swimming in, since its highly acidic water sits there at a deadly 70 degrees Celsius.

Upon following the path past the crater’s edge, we noted the concrete shelters in place for sudden eruptions. The smell of sulfur was at times overpowering, though some visitors seemed to want to carry the sensory experience home with them and sales of the volcano’s yellow rocks were clearly brisk.

The short walk led us to a dormant crater and more arid landscape before looping us back around to the car. Desperate to escape the overpowering odor of rotten eggs, we descended the mountain road down into Aso town.

A quick stop at the tourist office there, next to the main railway station, rewarded us with an incredibly detailed map of local eateries (bilingual to boot!). Ignoring their advice to patronize a nearby curry joint, though, we steered our car down tiny lanes to the edge of a cow pasture. There, in a beautiful wooden farmhouse, a restaurant named Olmo Coppia was serving up organic food I hoped would please my vegetarian visitors.

We took turns filching off each other’s plates — spicy chickpea curry, pasta with perfectly sautéed eggplant and lightly fried fu (wheat gluten) with dipping sauce — as we traversed the main courses. But it was the homemade ginger ale and hot ginger tea that garnered our votes for the cafe’s best dishes. Were it not for the slightly hefty price, a second (and third) round would have come naturally.

Postprandially, we took the road meandering north through gentle hills that offer wide-open views of the Aso crater at our backs. The rolling terrain, though mostly devoid of trees, was covered in fuchsia-colored cosmos — sparks of color amid the monochrome.

The woods began again just before the next range of mountains, providing the perfect setting for the idyll of Kurokawa Onsen. A nitch in the landscape hides just over a dozen ryokan dotted along the banks of the Chikugo River. Despite the apparent distance from so-called civilization, the inns and baths there are no haphazard shacks but top-notch retreats with comfortable tatami rooms, excellent nosh and likely some of the region’s best hot-spring baths.

We’d booked accommodation outside the village at the Hozantei Ryokan, where they offered a nicely priced room with its own private rotenburo (outdoor hot spring). Although the property spread over quite a few acres, with a duck pond and a forest path, its rooms that numbered fewer than 10 ensured a tranquil experience.

With a little time to kill before dinner, we drove the short distance back into town, grabbing a free parking spot at the tourist office, where all-comers can buy a tegata — a wooden plaque that’s a pass for one-day’s bathing at up to three of the village’s onsen.

At ¥1,200, it’s a decent deal, but with a host of baths awaiting us back at our own ryokan, we chose instead to pop into one or two of the main inns and pay their one-off ¥500 fees. The baths at the lovely Kurokawa-so inn near the main road were a tad too hot for my taste, but the secluded springs at Ryokan Yamamizuki made me want to linger long indeed.

Nonetheless, we were back on the dot for our dinner at Hozantei, and its feast of local specialties — horsemeat sashimi and mustard-stuffed lotus root, among others — left no one wanting.

That evening, though my husband and friends had had their fill of hot springs, I chose one final dip in the inn’s public bath. The air was brisk and the moon on the rise as I sank into a pool beside the river bordering the property. Mount Aso may loom over this region as a constant threat, but there are undeniable benefits to traveling — and living — in Kyushu’s “fire country.”

Check www.aso.ne.jp/~volcano/eng/ before setting out to see if the Nakadake crater is accessible via a toll road (¥500) and ropeway (¥1,000) to its rim, or whether noxious or poisonous fumes are rendering it inaccessible. For those on public transport, buses between Kumamoto and Beppu stop at both Mount Aso and Kurokawa Onsen.