- You’d better not be claustrophobic if you attempt this insane marathon.
How deep would you be willing to sink? Very deep, if you’re a marathon runner.
A group of marathoners recently set an unusual world record. They didn’t run the fastest or the longest.
Instead, they ran the deepest.
The 55 runners broke the world record for a marathon run at the greatest depth underground on October 25, 2025. They jogged along at a total depth of 3,669 feet and 10 inches.
To put that in some kind of perspective, that is deeper than two Empire State Buildings stacked on top of each other, or more than twice as deep as the Baltic Sea. The lift ride down into the depths took the runners three minutes.
You might expect the deep underground to be a nice and cool environment to run, but you’d be wrong. The runners faced a hot and difficult run, yet they concluded it nonetheless.
“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,” Bear Grylls (of pee-drinking fame), one of the event’s sponsors, told Guinness World Records.
The Depths of Sweden
But where on earth would you find a suitable location for this super-deep marathon? Well, not on earth, if we’re being specific.
The venue for the run was the Garpenberg Mine in south-central Sweden. Mining in the area dates to prehistoric times, but the current mine was started in the 13th century as an iron mine.
It has only expanded downward ever since. Today, it’s the world’s most productive zinc mining facility.
Garpenberg’s mineshafts stretch down to a depth of nearly 4,600 feet underground. Those deepest parts aren’t suitable for running a marathon, though, as that requires a somewhat flat surface.
Instead, the marathon took place roughly 1,000 feet closer to the surface. There, the marathoners found a suitable set of corridors that formed a loop.
Of course, there’s no endless straight line down there that would allow the runners to go from point A to B. Instead, to complete a marathon’s required 26.2 miles, they had to jog through the route 11 times.
And even then, the route wasn’t completely flat. There were some stairs and ramps that the runners had to navigate, which added another layer of challenge to the route planning, as the organizers needed to account for verticality when calculating the distance.
‘Hot, Humid, Dusty’
The conditions down the depths weren’t particularly suitable for a comfortable marathon event. Or does running a marathon on a muggy summer day without even the faintest breeze sound nice to you?
The temperature down in the mineshaft was a steady, balmy 75 degrees. Meanwhile, the ambient humidity stood at 72%.
And then, of course, you are in a mine, so there’s dust and stone particles and other things floating in the air.
“It’s hot, it’s humid, it’s a bit dusty, but we’re good,” one runner summarized.
What’s more, the runners faced what’s known as “cave silence.” If you’ve ever been on a cavern or cave tour where they turn the lights off and tell you to be quiet, you know what we mean.
There’s absolutely no light or sound down there. The marathoners had to prepare mentally for running in a completely silent environment with only the headlamps of their helmets piercing the pitch-black darkness.
Oh yeah, they had to run with helmets on, too. It is a mine, after all.
Charitable Run
Yet, despite the challenge, all 55 runners successfully completed the world’s deepest marathon. Some described most of it as feeling like an “uphill,” but they didn’t give up.
“No human has ever run this deep before,” one of them stated matter-of-factly after the run.
And indeed, they’re right. The group absolutely trounced the previous deepest marathon, which was completed at a measly 1,640 feet below sea level in the Crystal Mine in Sondesrhausen, Germany.
At the same time, they set a second record. The group also broke the record for the deepest underground marathon distance run as a team.
While they were at it, they were also doing some good. A fundraiser organized during the marathon raised more than $1 million for Gryll’s BecomingX Foundation, which provides education to youths in South African mining communities, and the Wild at Heart Foundation, which funds animal welfare projects around the world.
Want to learn more about ultra-deep places on the planet? Check out our list of the 10 deepest manmade structures ever built. Or, for additional marathon weirdness, read the story of the runaway goat that joined a marathon.