At the top of a steep path through a birch forest in western Sweden a middle-aged woman calls out “Välkommen!” with such warmth it’s as if we’re long-lost relatives being welcomed. We’re extremely happy to see her, too, and her trays of torn-up cinnamon buns, gherkins and crisps, the Swedish take on a pit-stop, which will power us on to the next feed station.

My 12-year-old son and I have come to the coast of Bohuslän, Sweden’s westernmost province, featuring a stunning archipelago of more than 8,000 islands stretching from Gothenburg to Norway, to take part in the Icebug Xperience. This is a three-day event in which participants either run or hike (or both) between 21 and 30km (13 to 18 miles) a day.

Lured by pictures I’d seen on social media of runners silhouetted on pink granite cliffs amid purple heather and hazy seascapes, I first planned to enter before the pandemic and was going to put my sons in the event’s kids camp while I ran – sailing, crab fishing and mini hikes keep little ones entertained. But then my eldest got into running, at first through parkrun, then an athletics club and took a shine to cross country, so asked if he could join the main event. Under 15s are allowed to take part, as long as they’re accompanied by an adult. So we’ve come on a mother-son trail running adventure.

The Icebug Xperience started as an ultra-race 10 years ago, before morphing into today’s more gentle multi-day event. It’s billed more as a memorable experience in a beautiful, rugged landscape than a race, and while there are some fast runners at the front, there are plenty of relaxed hikers of all ages at the back. About 850 people of all ages take part, divided into groups according to whether they are hiking, running or both. Our group ranged from a 75-year-old to my son, with several teenagers and plenty of people in the 40-60 bracket. Most entrants are Swedish or Norwegian and returners, but we also meet an Irish couple, Canadian sisters and Belgians.

Our base is Ramsvik Stugby and Camping, outside Hunnebostrand, where about half the participants are staying in a series of red cabins built on the waterfront. After a good night’s sleep, we’re ready for the first stage, Hunnebo Haute, a 21km stint. We plan to run the first half and walk the rest, partly because I’m worried about how my son’s legs will cope over the three days, not to mention my own – while I run fairly regularly, I don’t normally do much beyond 10km. The adrenaline means that the running part passes in a happy blur of trees and sheep and rock-strewn paths and hillsides, but the walking section through the forest drags. The signing is great though, so we never fear getting lost, and regular food stations, with their smiling volunteers, offer welcome respite.

We run the final stretch along the coastline over smooth weathered rock and bouncy wooden jetties until we reach the pretty port town of Hunnebostrand. On the boat trip back to camp we tuck into a carb-heavy vegetarian salad box. A swim in the sea eases aching feet and legs and we watch a wind-down yoga session on the golden-lit beach from a pontoon.

The Icebug Xperience takes place in early September, once the Swedish schools have gone back, so we pretty much have the campsite to ourselves. Hearty breakfasts and dinners are included in the package and the evenings are convivial. This year’s event will include food trucks, music and an outdoor cinema.

On day two, poetically titled Woods and Islands, after a short bus ride to the start, we decide to take a sanctioned shortcut to keep the distance to 20km instead of 30km. My son’s worried it’s cheating but I’m conscious of his age and remind him that running just over 60km in three days will still be a huge achievement.

We also resolve to run the whole thing but slower, at what the Swedes call snacka-tempo or chatting pace. It’s lovely to get time alone with him, especially since he has started secondary school with all the associated swagger and testosterone that brings. I like that this is challenging us both in different ways, him on the endurance and mentality front and me on speed and fitness, but we’re getting through it together.

We begin to adopt some tactics the more seasoned participants employ, namely foraging for berries wherever possible and walking up the hills and sections with big boulders, which until now we had been charging through. It makes a big difference to our energy levels. Still, by the time we finish in the middle of the afternoon, we’re fairly broken, and return to the campsite for an ice-bath swim and dinner before collapsing into bed early.

The final day, Ramsvik Rocks, is 26km and the toughest on our tired legs. But it’s by far the most spectacular in terms of scenery, which provides a welcome distraction. We start on one island passing the brightly coloured painted houses of Smögenbryggan, then cross to the mainland. We scramble through thick forest and then, with 10km to go, we cross the swing bridge on to Ramsvik. Eventually we find ourselves running on the stark pink granite boulders that I’d first seen in the pictures and which give today’s stage its name. The shiny blue sea sparkles all around us.

Despite the views, our morale dips at times and at one point I wonder whether we’ll ever make it to the end, but we do, crowds with cowbells clanging us in and cheering as we finish on the sandy beach. The campsite has an air of quiet contentment and deep exhaustion, but my son is beaming as Swedes of all ages come over to congratulate him. I’m tired but happy – and very proud of us both.

• The trip was provided by Visit Sweden and Icebug Xperience. The event runs from 1-3 September. Entry starts at £201 per person (less when booked in advance), and cabin accommodation packages at Ramsvik Camping currently start at £367 per person for three nights, or £436 per person for four nights with breakfast and dinner (and a sauna). For more information on Bohuslän visit vastsverige.com