Runners strap headlamps on to tackle deepest marathon over 3,000 ft underground
“It’s hot, it’s humid, it’s a bit dusty, but we’re good.”
That’s how one of the runners taking on the deepest marathon ever described the conditions.
With their laces tied tightly and headlamps fixed in place, 55 runners from 18 countries took on a certified 42.195-km (26.2-mi) course a whopping 1,118.56 m (3,669 ft 10 in) underground.
To help you understand the depth, it’s somewhere in between the height of Angel Falls, the world’s tallest waterfall, and the UK’s highest mountain Ben Nevis, in Scotland.
The record-breaking marathon was a joint venture between BecomingX (UK), ICMM (UK) and Boliden (Sweden), and took place in Garpenberg, Sweden, on 25 October 2025.
The team ran 11 laps around the route and raised around $1 million for charity in the process. The event also earned them a second world record title for deepest underground marathon distance run (team) with a total of 1,082.30 m (3,550 ft 10 in).
Bear Grylls, a co-founder of learning and development company BecomingX, said: “A marathon, hundreds of metres underground. Well, that would be extraordinary, but also we’ve got to kind of stay within the realm of the possible.
“Marathons are hard in temporary environments. You go into this environment, you clock in the fear and the adrenaline, the intimidation of the environment – it definitely takes it up a few notches.”
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Runners taking part in the record-breaking event described just how difficult it was.
It was so far underground that the lift took a full three minutes to go from the surface down to the starting line.
“Even if you just stop and wait three minutes - it’s a long time,” one said.
While another described much of the run as “uphill” and a third said: “No human has ever run this deep before.”
The previous deepest marathon was the Crystal Mine Underground Marathon, run in an old salt mine located 500 m (1,640 ft 5 in) below sea level in Sondershausen, Thuringia, Germany.
