It's not every night you get to dine at a fancy restaurant – in your pyjamas. But that's exactly what I'm doing in the dining room of Hoshino Resorts KAI Aso, a boutique hot-spring resort in the volcanic heart of Kyushu, the southernmost of Japan's four main islands.
Actually, they're not technically my pyjamas. Like other diners around me, I'm dressed in KAI Aso's version of "onsen wear": mauve cotton PJs, a soft grey linen yukata, grey split-toe socks to wear with a pair of wooden thongs, and a short quilted coat (we're 1000 metres above sea level so nights can get chilly).
Clip-clopping back to my room after dinner that first night, I feel quite the geisha.
When I say "room", I mean freestanding villa. There are just 12 of them at KAI Aso, each with a Western-style bedroom (real beds, no futons), a tatami room for relaxing, a lounge room with skylights and timber floors, and sliding glass doors opening onto the surrounding forest.
It's outside that I find KAI Aso's real drawcard, the reason people come to this boutique resort within Aso-Kuju National Park. It's my own private bath built into a timber deck and filled continuously by 40-degree spring water.
Throughout my two-night stay, every chance I get, this is where you'll find me: chin-deep in clear, volcanically heated water, preferably with the late afternoon sunshine twinkling through the trees and a bit of birdsong. It's "forest bathing" taken to a whole new level.
Lest I par-boil myself, a 10-minute "hour glass" is provided. That's the ideal length of time for a soak, according to the "art of bathing" guidebook on my coffee table, which includes information about the mineral content of the water, how volcanoes create hot springs, deep breathing techniques, even in-bath stretches.
Like Hoshino Resorts' 14 other KAI hot spring resorts around the country, helping guests connect with their surroundings is part of the KAI Aso ethos. .
So on my first morning I try "mountain-air breathing" at 7am, a sort of standing yoga class outside the main building, with misty mountain views. This is followed by breakfast in the company of five mountains that resemble a sleeping Buddha, including Kyushu's highest peak, a 1791-metre active volcano called Nakadake. There are free springwater- and sake-tasting sessions throughout the day, too.
The spectacular 9-course "kaiseki" dinner, included in the room rate, not only highlights local, seasonal produce but presents them in volcano-inspired ways: there's wagyu flambeed on a heated lava plate, for example, and a dessert that requires me to pour mandarin-flavoured "magma" over a cheese mousse "caldera" on a plate sprinkled with macha powder to resemble its grassy interior.
Then there are the area's attractions, best reached by rental car: Aso Volcano Museum, Aso Shrine and hot spring towns such as Yufuin and Kurokawa Onsen are all less than an hour's drive away; horse-riding across the very un-Japanese pampas-grass plains inside the caldera is also popular. Across the road from the resort there are half a dozen cafes, the pick being Chez Tani, a French-style patisserie offering coffee and cakes with a side order of volcano views.
KAI Aso's in-house Caldera Bar experience is another must. Over complimentary drinks, a guide explains how Aso caldera, one of the world's largest, was formed 270,000 years ago. The 30-minute session ends with a hands-on experience that involves burying a partly filled balloon in a box of flour then pricking it with a pin. Pfft! The air escapes and the flour-mountain slumps, creating – ta da! – a miniature Aso caldera.
Checking out on my last morning, wearing my own clothes again, I watch other guests tottering to breakfast in their yukata and wooden thongs, and think: more hotels around the world should do this. Because nothing says, "Sunday morning", no matter what day it is or how old you are, like breakfast in a hotel restaurant – in your pyjamas.
Cathay Pacific flies daily to Fukuoka via Hong Kong from Sydney, Melbourne and other capitals. See cathaypacific.com Hoshino Resorts KAI Aso is two and a half hours by bus and taxi from Fukuoka airport, or 70 minutes by taxi from Kumamoto airport. Contact KAI Aso for more information.
Hoshino Resorts KAI Aso has 12 villas, each with its own private hot-spring bath. Rates start at 39,000 yen (about $500) per night, per person including dinner, breakfast and Wi-Fi. See kai-ryokan.jp
Louise Southerden stayed at her own expense with flights from Walk Japan.