In the pitch-black tunnels of Boliden’s Garpenberg zinc mine, over a kilometer below the surface of northern Sweden, 55 runners from 18 countries gathered to compete in one of the most extreme races ever attempted — the World’s Deepest Marathon.
The course, carved through the humid, diesel-scented rock 180 kilometers northwest of Stockholm, spanned a 2-kilometer stretch of tunnel that participants ran back and forth 11 times to complete the full 42 kilometers. Among them were mining executives, Boliden employees, ultra-marathoners, and first-time racers.
“You’d run to the end and then turn around — 11 times,” said Henrietta Newman, a consultant with the World Gold Council who took part in the event. “Other than our headlamps, it was complete darkness.”
The marathon, organized by BecomingX, the International Council on Mining and Metals, and Boliden, is expected to enter the Guinness World Records as both the deepest marathon and the deepest underground marathon distance ever completed, pending verification. The event also had a charitable mission — raising over $1 million for the BecomingX Foundation, which supports education in Africa, and for dog welfare projects run by the Wild at Heart Foundation.
Runners descended by elevator to 1,120 meters below sea level before being driven by truck into the tunnels. Despite being inside an active mine, organizers ensured safety: helmets were mandatory, though participants wore running shoes after the course was smoothed for the event. “I was worried about the hard hat,” Newman admitted, “but it was actually super light.”
Conditions underground were challenging. The air was thick and humid, around 24°C, but also contained 30% more oxygen than at the surface — a small advantage against fatigue. “Coming down the incline, you’d get these occasional puffs of air, and it felt amazing,” Newman said.
Though well-supported with hydration stations and logistics teams, the unique environment tested endurance. Even the top finisher completed the course about 50 minutes slower than his personal record.
For many, however, the sense of camaraderie outweighed the discomfort. Newman described a heartwarming moment when a group of South African runners doubled back to accompany a first-time marathoner on her final lap. “It was just such a nice moment,” she said. “There were people from all walks of life, and everyone helped each other finish.”