Through the dense steam rising from the onsen, Jupiter is clearly visible over the twinkling black waters of the Seto Inland Sea. It's not hard to see why this hotel is called Bella Vista; it lies tucked into the hills outside the historic town of Onomichi, commanding sublime views of the sea's misty islands. What's more, the onsen is open to the elements, allowing fresh sea breezes to caress the skin of bathers as they boil themselves blissfully to a jelly.
The islands are part of the Seto Inland Sea National Park, which is celebrating its 80th anniversary this year, making it one of Japan's three oldest national parks.
Tomorrow, my wife and I will be motoring across that sea, via the Shimanami Kaido, a spectacular 60km road and bridge network connecting Japan's main island of Honshu to Shikoku (the country's fourth-largest island). Starting here in Onomichi, in Hiroshima prefecture, the route will take us across six smaller stepping-stone-like islands before arriving way down in Imabari (Ehime prefecture).
ONOMICHI IS A delightful old port town, packed with ancient temples and literary connections. It's built on a hill-side overlooking the sea, and the top of Senkoji Hill, which towers 500 feet (150m) over the inhabitants, offers stunning panoramas. The ascent by ropeway is short but breathtaking and a steep, winding trail known as the Path of Literature leads you back down.
Along the path, and dotted among fragrant, cicada-loud pines, are 25 boulders, all of which are inscribed with quotations from famous writers who have lived here over the centuries. Halfway down lies the vermillion-lacquered majesty of the Senkoji Temple. Established in 806, it's one of Onomichi's most iconic symbols, and one of Japan's oldest places of worship.
By the time we reach the bottom, we're ready to sample another Onomichi icon: ramen. One of the most famous ramen shops is the Tsutafuji, a tiny mum and dad waterfront bar near the JR station that's been in business for more than 50 years. A quick peek behind the noren curtain reveals just 10 stools, clustered around an L-shaped bar. Consequently, there's always a queue outside. Waiting customers have brought manga to read and Nintendo games for the kids, to pass the time. Once inside, the cook simply asks "large or small ramen?" - and we're immediately given a steaming bowl of noodles topped with generous slices of pork in a piping hot pork-bone-and-fish broth.
As soon as we're across the Onomichi Strait and onto Mukaishima, island time kicks in: traffic evanesces, the pace slows and we find ourselves in a dreamy realm of citrus groves embosomed in the folds of mountains, dark green foliage contrasting with the sapphire sea.
Citrus is big business here, from mikan tangerines, oranges and lemons to hybrid fruits unique to these islands, such as hassaku and anseikan (a cannonball-sized grapefruit). Setoda Island is Japan's No1 producer of lemons, while Ehime prefecture is known as the Orchard of Japan. Mikan trees even adorn the roadside verges.
"If you go to Setoda, you must try the lemon ice cream," insisted the desk clerk at the Bella Vista. Citrus-related cakes, jams, honey, sauces and juices abound, too.
As we pootle across the bridges (all seven of them), a head-spinning seascape of endless islands unfolds below us. With no traffic behind, I slow the car to a crawl to get a better look at inhabited islands; desert islands; islands that are no more than a rock with a tufty pine tree clinging to it. And all the while trawlers, tugs and speedboats put-put to and fro.
The bridges themselves are magnificent structures, rising out of the placid waters and towering above the somnolent scenery. Tatara Bridge is the world's longest cable-stayed bridge. Its elegant 220-metre-high steel towers represent the folded wings of a crane. At 4,045 metres long, Kurushima Bridge is the longest suspension bridge in the world. It takes us a full five minutes to cross it.
The bridge network may have improved connections between the once-isolated island communities but any detour from the Expressway takes you deep into the heart of rural Japan: unbroken greenery save for occasional clusters of houses; little white-eye birds darting among the branches of the cherry trees; kites swooping low, then wheeling away again.
Yet, for a rural idyll, there's a surprising amount of art and culture to enjoy.
The Kosanji Temple, on Ikuchijima Island, was built in 1936 by Buddhist priest Koso Kosanji in memory of his mother. The surrounding wonderland of pagodas and gorgeous gardens took more than 30 years to complete. The buildings are modelled on famous temples from different eras in Kyoto, Nikko and elsewhere, so it's like taking a stroll through Japanese history.
By the time we make it across the Kurushima Bridge to Imabari, where the Bridge Road ends, the sun is slip-ping and the islands are floating in a sea of mist. We pull into a rest area to savour the serenity of the moment, the sea breeze tugging at our hair as we contemplate the boats threading their way in and out of the islands towards the open ocean.
Although the Shimanami Kaido is an expressway, it has been designed with the cyclist in mind. There are bike and pedestrian lanes along the whole length, so you can quite literally walk across the sea. Moreover, with 14 cycle-rental terminals along the way, you can go at your own pace. If you get tired, just hand in your bike and hop on a bus.
More good news for cyclists is that, as of March 22, Onomichi has been home to Japan's first hotel designed exclusively for cyclists, which is just five minutes' walk from the JR station. In Hotel Cycle, you can park your bike in your room, and there's even a cycle-through restaurant.
From now until October, to celebrate the 80th anniversary of the Seto Inland Sea National Park, the Shimanowa 2014 campaign will be putting on dozens of events to promote the charm of the islands, culminating in a huge cycle marathon on October 26, in which, it is hoped, 8,000 people from around the world will participate.
Getting there: Cathay Pacific flies daily from Hong Kong to Tokyo's Haneda Airport. From Haneda, there are several All Nippon Airways flights a day to Hiroshima Airport, from where it is 15 minutes by bus to JR Shiraichi Station, then 40 minutes from Shiraichi to Onomichi Station on the JR Sanyo Line. Alternatively, it takes about three hours and 40 minutes from Tokyo Station to Fukuyama Station on the JR Tokaido-Sanyo Shinkansen Line, then 20 minutes from Fukuyama to Onomichi Station on the JR Sanyo Line.