TIM MARKLOWSKI – A triathlon across Corsica and Sardinia – Runner’s World, May 2026 issue

Most people don’t spend their honeymoon plotting future trips that will take them away from their new spouse for weeks on end, but that’s where Tim Marklowski’s mind went as he travelled the Italian coastline with his wife last year. The couple spent five months sailing and rock climbing together – plenty of time to think about the next adventure. When their boat crossed the Strait of Bonifacio, the 11km gap that divides the islands of Corsica and Sardinia, he wondered if anyone had ever swum it.

Turns out it’s a fairly regular challenge for serious swimmers, despite currents and rough seas making it only sporadically crossable. What no one had done before, however, was attempt to travel from the northernmost point of Corsica to the southernmost of Sardinia, adding the islands’ two toughest hiking trails to the challenge.

Tim conceived a multi-section triathlon for September 2025: bike-run-bike-swim-bike-run-bike from Barcaggio to Spiaggia Su Giudeu, the runs taking place along the 180km of the GR20 hiking trail in Corsica and the shorter but more treacherous 40km Selvaggio Blu (‘Wild Blue’) on the eastern coastline of Sardinia. The latter is unmarked aside from the odd cairn, has no water points and includes rock climbing and abseiling sections in addition to those that are vaguely runnable.

His four separate bike rides totalled 640km on roads, and the swim, as it wasn’t between the absolute closest land points, was 13.1km in 4 hours three minutes – including dodging jellyfish and some pauses to throw up from seasickness. All in: 873km and 25,000 meters of elevation gain in 12 days.

However, strictly speaking an additional four days should be added to his time, a tense wait for the strait to be swimmable which thankfully also allowed him to recover from a leg injury sustained on the last of five days on the GR20. Although he was first, Tim doesn’t mind that someone else will probably do it faster in future. ‘For me it was more about bringing together everything I’ve learned in the past decade: rock climbing, sailing, swimming, and so on. I like to be an all-terrain animal,’ he says. ‘It was also about trying to show that you can do big, creative challenges in a more ecologically friendly way, without flying somewhere. You don’t need to go to the Himalayas.’

Outside of this challenge, Tim’s whole 2025, including his day job, was centred on outdoor adventures. Born in Bavaria, he’s now based in Bern where he has worked since 2022 as an IFMGA-qualified mountain guide. With clients, last year he also spent a month ice climbing in Italy, tackled the North Face of the Eiger, and tried to get from Switzerland’s lowest point to its highest within 24 hours by cycling, running and climbing from Lake Locarno to the summit of Dufourspitze. They were a frustrating 23 minutes over the self-imposed deadline.

If it sounds like he might not have much time for running, he says it’s always been part of his exercise mix. ‘It might not be my main focus, but since I was a child there has never been a time when I didn’t run. It’s always been there.’ He trained for the Corsica/Sardinia challenge by running up to meet his clients at mountain huts. He got ready for the island crossing through swims of up to 10km in his local pool, and didn’t specifically train on the bike, ‘Other than to get my butt used to the saddle,’ assuming that the other activities would give sufficient fitness. He loved the difference between the GR20 and the Selvaggio Blu. ‘Running and hiking in Corsica was more mountainous, almost alpine and pretty cold,’ he says. ‘Sardinia felt more Mediterranean and also wilder, and you feel more like you’re on an island because the trail is along the coastline.’

He describes finishing the challenge as ‘pretty unspectacular’, arriving at the bottom of Sardinia on his bike on his own in the dark, on the phone to his wife so as not to feel completely alone. ‘I touched the water and then realised I had booked my accommodation for the night six kilometres away – stupid!’

But this was the kind of adventure he wanted: solitude in truly wild nature, not an organised race, and not a million miles away from home. ‘It was hard, but it also had a sort of relaxing side to it,’ he explains. ‘You have a structure, but within that structure you’re completely free, especially if you’re alone. It was really relaxing for the mind. For me it was like a vacation for the head.’

FIVE THINGS TIM TOOK ON HIS TRIATHLON

Bike: Cube Agree 62 SLX with Cyclite bike bags

£4,199

Tim found this high end road bike second-hand, an aerodynamic ride with a carbon frame for his long journeys across the islands.

Backpack: Black Diamond Distance 15L

£112

Black Diamond’s hybrid pack has ‘suspension’ for running as well as extra storage for mountain treks.

Shoes: La Sportiva Prodigio Pro

£170

With a 6mm drop and 4mm lugs, this shoe is aimed at ultrarunners who also want some speed.

Wetsuit: Zoot Kona 2.0

£328