On this windless autumn Saturday, the landscape is curiously hushed. Occasionally, a tiny chorus of coal tits gathers to chat in the pines above my head, but otherwise it’s soundless, the muffled stillness willing me to slow my pace. As the track turns from soil to sand, I skitter over smooth grey rocks to reach a crescent of chalky powder. As I strip down to my swimsuit and slip into the shiveringly crisp water, the sun breaks through and I’m suddenly swimming through rhinestones, amazed to have the coastline to myself.

I’m hiking, solo, two hours south of the Swedish capital, along the Stockholm Archipelago Trail, a 167-mile (270km) path that has been gradually opening, section by section, this summer before its official launch later this month. It came about thanks to a chance conversation between Marie Östblom, a project manager for the Stockholm Business Region, and Swimrun co-founder Michael Lemmel, and when all sections are completed later this month, the trail will run between Arholma in the north and Landsort in the south, linking 21 islands.

I’m trying out a three-day section of the route at the beginning of what Östblom calls the archipelago’s “magic season” – September, October and early November: “You get those gorgeous misty mornings but the sun is shining, the leaves are turning gold and the evenings get darker earlier. It’s a chance for cosiness after all the summer light.”

The fact that so few people are here to enjoy this season is one of the reasons the trail has been developed. The archipelago’s tourist season is short, running mainly from mid-June to mid-August, the Swedish school holiday period. While there is year-round access, fewer ferries run outside those months and many guesthouses and restaurants close. It’s hoped that the trail will help stretch the season, increase footfall and give local businesses reason to stay open longer.

“Making the trail is just the start,” says Östblom. “It would be great if small taxi boats grouped together and designed a booking app, like an archipelago version of Uber. Or if guides, accommodation and bike and kayak hire operators worked together to make trail packages.”

For now, visiting in the magic season means plotting a route around the available transport. To reach the three southern islands I’m hiking I’ve taken a train to Nynäshamn, an hour or so south of Stockholm, then a water taxi for the 25-minute hop to Nåttarö (though many of the northern islands can be reached directly by ferry from Stockholm year-round).

Thanks to Sweden’s allemansrätten, or right to roam, it is possible to visit all year if you bring your own tent and supplies. I, however, am slipping in just before the cabins here close for the season.

I’m met on the pier by manager Carina Ljung. Nåttarö is a car-free island with the archipelago’s largest sand beach but no year-round residents, and offers what Ljung calls “a traditional Swedish summerhouse experience”, with 49 charmingly back-to-basics cabins, a campsite, hostel, restaurant, grocery store and bike/kayak rental shop. “Staying here reminds people of their childhood,” she says, adding that with no insulation in those cabins and shared showers and compost toilets, they are “very open to the weather”.

Happily, the weather is living up to the magic season tagline. Like most of the trail, this seven-mile section is a loop, so I can drop my bags in my cabin and walk carrying only a daypack. Within two minutes of shutting the wendy house-like cabin door I’m alone in that silent forest, following the trail to magnificent Stora Sand beach.

Further on, the terrain switches from desert island to Zen garden as I pick my way over smooth, moss-cloaked boulders to the island’s highest point. Nåttarö is a nature reserve and, as beams of sun shine on birch leaves and pine needles, and deer spring noiselessly over heather and lichen a few metres away, it feels more garden of Eden.

That evening I sit on the terrace of Nåttarö’s one pub/restaurant as the setting sun paints a streak of bright lingonberry across the sky. I pull a blanket over my knees and enjoy rich fish stew before picking my way back to my cabin in the moonlight.

Next morning, I catch a waterborne lift with Carina’s husband to continue the trail on nearby Ålö. Though this island is more easily reached than Nåttarö, with year-round ferries and accommodation, it is just as quiet. In warm sunshine, here the trail feels like an extended forest bathing experience, as I tune in to whispering pines, rustling birch leaves and the soft slap of water on pebble. I’m soothed by every step as I leave the shoreline behind, following yellow and blue trail markers up into the forest (the markers’ reflective bands make the trail feasible with a head torch in the months of early dark) then back down to a plateau of boulders so close to the water’s edge that it feels like walking on water.

At Ålö Stora sand, I stop for a swim. Afterwards, dragonflies flutter around me as I eat a sandwich brimming with dill and fat prawns. In summer, the picnic benches and campfire here would be thronged with families. Now, I have them to myself. As I soak up the autumn sunshine, the setting is so soporific that I’m shocked when seven neon “seals” – actually a group of cap-wearing swim-runners – suddenly appear offshore.

Returning to the trail, I pass a wetland area and bird-viewing platform before dipping back into forest to reach today’s dramatic finale – a broad clifftop with such a wide-angle view that the islands look like a floating jigsaw waiting to be pieced together.

That evening I meet Thomas Hjelm for dinner at Utö Värdshus, an elegant inn above Gruvbyn, the historic village at the centre of Utö island that, with its luxury yachts and red-timbered houses, has a hint of “Scantucket” about it. A resident of Utö, Hjelm was involved in the creation of the trail and hopes it will encourage visitors to explore the island.

“The trail will also be good for us locals,” he tells me as I tuck into a plate of pan-fried kingfish with velvety artichoke puree and red cabbage. “The more people are here, the more they will spend at the shops and on the ferries, which creates employment.”

Of course, local people can enjoy the trail, too. “There’s one bench we’ve installed by the water that I love,” Hjelm says. “It’s hard to sit still but if you do, something happens. After 15 minutes you hear and see more. After 90 minutes, you don’t want to leave.”

The next day, as I follow the 11-mile stretch of trail around Utö, I come to what must surely be Hjelm’s bench. The wind dances through the reeds beside me and flecks of sunlight tug at the glassy water ahead. As I gaze at the horizon, it feels less like observing a landscape than being immersed in it. Is it the bench I don’t want to leave, I wonder, or the trail?

The trip was provided by Visit Sweden, including train travel from the UK to Stockholm. For information on the Stockholm Archipelago Trail, see stockholmarchipelagotrail.com. Also see visitstockholm.com