Fifty-five runners from 18 countries participated in a certified marathon spanning 42.195 kilometres.
Running a marathon is already a tough challenge, but a group of runners recently took it to another level by completing a race deep below the ground. According to Guinness World Records, in a unique event held in Sweden, dozens of participants ran a full marathon course more than a kilometre underground.
Fifty-five runners from 18 countries participated in a certified marathon spanning 42.195 kilometers (26.2 miles), held at a depth of 1,118.56 meters (3,669 feet 10 inches) below the earth’s surface. Tying their shoelaces tight and wearing headlamps, the runners completed this unique race deep within the earth.
One of the participating runners said that the atmosphere was hot, humid, and slightly dusty, but they managed well.
To illustrate the depth of the race, it was noted that this subterranean level lies at a depth equivalent to the vertical distance between the world’s tallest waterfall, Angel Falls, and the UK’s highest mountain, Ben Nevis, in Scotland.
This record-breaking marathon was organised through a collaborative effort by BecomingX (UK), ICMM (UK), and Boliden (Sweden), and took place on October 25, 2025, in Garpenberg, Sweden.
The runners completed 11 laps of the course, raising approximately $1 million for charity in the process. Through this same endeavour, they also secured a second world record-for the deepest underground marathon distance covered by a team-registering a total depth of 1,082.30 meters (3,550 feet 10 inches).
Bear Grylls, co-founder of BecomingX, stated that organising a marathon hundreds of meters underground is an extraordinary feat, yet it is essential to ensure it remains within the realm of possibility. He noted that a marathon is inherently difficult even under normal conditions; entering such an environment exposes participants to fear, adrenaline, and the atmospheric pressure of their surroundings-factors that further heighten the challenge.
