In a town of 20,000 people, a train station should not be difficult to find. But Kiruna is like that; up here, 100 miles inside the Arctic Circle, the quotidian can be surprisingly elusive. In summer, Kiruna has months of midnight sun; in winter, perpetual darkness illuminated only by the aurora borealis. A hotel nearby gets rebuilt annually, entirely of ice. Soon, the town will even have a spaceport. But not, it appears, a train station.

With half an hour before my train leaves, I try my halting Stockholm Swedish on two men unloading goods into a warehouse on the edge of town. One of them points at a bus station 50 yards away, backed by leagues of open plain.

“No, no—the train station,” I say.

“One mile away,” he responds. “You have to take the bus.”

The mistake is mine. Anybody who’s been to Kiruna knows that what you’re looking for might already be elsewhere, because anybody who’s been to Kiruna already knows that the most remarkable thing about Kiruna isn’t the midnight sun, or the northern lights, or the ice hotel, or the spaceport.

It’s the fact that the town is moving.

* * *

Kiruna’s move—three kilometers east, street by street, over 17 painstaking years—owes to the same thing that caused the town to spring up in the first place: a seam of iron ore that currently provides 90 percent of the iron for all of Europe, at a rate of more than six Eiffel Towers’ worth a day. More than a century after mining began, nobody knows quite how deep the seam runs. What is known is that the ore lies at an angle. For more than a century, the Luossovaara-Kiirunavaara mine has not just been getting deeper; its underground detonations have been shifting laterally, exploding rock into the gaps left behind by the extracted iron, and causing cracks to appear on the surface above. In recent years, those ominous fissures have been edging ever closer to the town.

Kiruna is, quite literally, being undermined. The mine isn’t going anywhere, so the town has to.

Recently, I visited Kiruna to see the mine and the town it would reposition. Knowing that the sun will still be up at midnight, spending your day in the depths of a mine makes more sense than it might a few parallels south. A tour of the mine lasts almost three hours. Some people on the tour were worried about claustrophobia, and as we rode a bus down the narrow, pitch-dark tunnels into the mine’s bowels, the worry seemed well founded. But as we reached a depth of 540 meters, the roadway opened into a cavernous space lit with the dull glare of a midnight hospital. There was a cafe, and a visitors’ center, and a tour guide about to repeat the same 5,000-odd words for what might be the 5,000th time.

All the numbers she shared are big: the number of years since the first spade struck rock, the number of trains that ferry the iron to the ports of Narvik and Luleå, the number of miles those trains travel, and the number of wagons hitched up behind them. The lengths are big, and the heights, and the widths, and the depths. Above all, the volume: the sheer mass of material that is blown out of this underground in any given unit of time.

We were shown the living conditions of the very first miners. We were walked through the crushing and grinding processes, after which the iron is spit into the sunlight. We were given coffee. Through a muddied convex sheet of safety glass, I saw some anonymous detritus being catapulted down a shaft. In what must be one of the world’s deepest-lying cinemas, we were shown what seems suspiciously like a promotional video aimed at prospective investors. Finally, we were each given a parting gift: a small plastic bag filled with tiny balls of iron.

One the way back to the center of Kiruna, the atmosphere on the bus was subdued. Maybe people were tired. But I think were all recovering from those numbers, too, pondering them as one ponders the stars. Kiruna never looked like a large place, but it now somehow looked small enough to move.

* * *

“The town and the mine live in symbiosis,” says Kiruna’s deputy mayor, Niklas Sirén. “There is no town without the mine and no mine without the town.” Sirén is almost right. The town and the mine are indeed symbiotic: Without either one of them, the other would be pointless. But at the risk of pedantry, the town isn’t there because of the mine—it’s there because of the iron. Without the iron there would be no settlement; without the settlement, no mine. These semantics are important. To say that the mine was there to begin with is to say that the iron was waiting to be extracted. But that’s not true.

Sirén makes the town/mine dynamic sound like an unwanted pregnancy: a relationship between equals that got out of hand, resulting in a major upheaval. It may look like that now, but it wasn’t always so. In the beginning was the iron. What developed thereafter was a system of causality that the sociologist Andrew Pickering calls a “dance of agency.”

Consider, as Pickering does, the Mississippi River: a behemoth that, once upon a time, fashioned its own three-foot banks of sediment. Occasionally prone to be overtopped, these natural levees by and large did a good job. But when the European settlers founded New Orleans, they decided to raise the levees. Flooding couldn’t be a rarity; it needed to be impossible. But the plan didn’t work. In response to the epic feats of human engineers, the water levels began to rise. And the rise has been remarkable.

The U.S. Army Corps of Engineers, Pickering reminds us, first noticed that the Mississippi was suddenly 30 feet higher than the river into which it runs. They attempted to regain control of the situation by building a giant weir. But when storms hit, the weir was battered. Soon it wasn’t merely the water and the levees that were rising, but costs—and, with them, concerns. (And we all know what happened next.)

The iron is Kiruna’s Mississippi; the mine, its artificial waterways. At a certain point, the mine began to threaten the very thing it was supposed to support. In the dance of agency, the mine took the lead; now, humans are wrestling it back.

* * *

Kiruna doesn’t look like it’s about to move. There are no cranes—at least not that I could see. No people in high-visibility jackets taking measurements along the streets; no piles of boxes accumulating in the central square. Behind the glass-covered balconies I imagined the people of Kiruna packing kitchen utensils, or taking picture frames from their walls—one a day, maybe one a week—in slow preparation.

That’s not how it works, of course. There won’t be one moving day; there will be thousands. Like a child, the town will change in increments. One day, people will look at it and notice that everything has changed, and wonder when that happened—how it could have happened like that, all in plain sight.

At one point on my visit, I sat on a terrace at a campsite overlooking the twin peaks of the mine, and my thoughts turned to lost cities, ghost towns: Prypiat, Kowloon, Atlantis. One poisoned, one disinherited, one swamped. Kiruna won’t join those ranks—not for a while, anyway. The town is being moved precisely in order to avoid such tragic, fabled company. But this Kiruna—the one I can see from here, under a sun that refuses to set—will be lost, chased into a new location by a proliferation of cracks.

When I do find the train station, it is small, and clean, and isolated. It’s not embedded yet; it hasn’t been here long enough. There are tracks that disappear into the north, but not for the train that I’m about to board. For today’s human cargo, this is the end of the line: one among the countless extremities of Europe’s great, webbed hand. It’s not the end of the world, but it’s close. In its way, it’s still a frontier. And because it’s a frontier, it’s vulnerable.

* * *

Eventually, back in my Stockholm apartment, I empty the iron balls from Kiruna into a small bowl. Dull grey spheres less than a centimeter in diameter. They look like they might be made of licorice, a popular delicacy here in Sweden. For the benefit of visitors, I wedge a little sign taped to a toothpick: “Do Not Eat.”

Sometimes, sitting at my desk—reading Pickering, perhaps, or thinking about the incomprehensible mountains of stuff we will continue to extract from the ground, and the disasters waiting to happen when we do—I pluck one of the balls from the bowl and look at it for a while. The poet William Blake once conjured “a world in a grain of sand”—and, in the very next breath, “infinity in the palm of your hand.” I’m not so sure. The world does perhaps lie in this tiny ball of iron, but it is today’s world, not tomorrow’s. One day, the iron below Kiruna will be exhausted, or else too costly to access. The town will not have to move again; it will sit there, abandoned, like the outposts of so many frontiers.