Onkalo is place no one should want to go. It’s a place that “should not be disturbed.” According to the opening narration of Into Eternity, “You should stay away from this place and then you would be safe.”

Onkalo is a nuclear waste repository in Finland. Here, filmmaker Michael Madsen lights a match as he begins to speak, so his face hovers in darkness and his glasses glint. “I am now in this place,” he says, “Where you should never come.” And yet, there he is, inside the tunnel, addressing you but also, more urgently, the future viewer of his documentary. This viewer might be tempted to open the vault and—unknowingly, presumably—let loose the toxic aftereffects of today’s nuclear energies. As he speaks and you listen, the facility is still under construction, the Finnish government’s response to the accumulating waste. “Onkalo must last 100,000 years,” he says, “Nothing built by man has lasted even a tenth of that time.”

Time is the point—of Onkalo and Into Eternity. Time and the costs of both remembering and forgetting. At once practically consequential and dreadfully abstract, time remains elusive throughout the film, though nearly every interview subject touches on it. For now, the process of securing nuclear waste involves water, which creates a seal for radiation. But as the waste floats in various facilities over the world, the designers of Onkalo have determined that a vault located 500 meters below ground, in solid Finnish bedrock, 1.8 million years old, will secure the radioactive materials for long enough—100,000 years—that they will no longer be lethal.

The problem is that no one can predict what will happen in that time, or who might come across the vault, or how they might respond to it. Will they be curious? As Mikael Jensen worries, one scenario is “that people even know it is dangerous but valuable at the same time,” much like the tombs of the pharaohs seem to us now. Will future discoverers of the vault be afraid or reckless, knowledgeable or ignorant, primitive or advanced? Will they have any notion of what the tunnel’s many different warning markers say? “There is no clear understanding,” the film submits. “It’s quite possible that we will not be understood by the future.” 

Such conceptual problems seem insurmountable. But the alternative—not conceiving, not tackling such problems—is worse. At least this is the thinking of the many experts who speak with Madsen, including Timo Äikäs, Executive Vice President of Engineering at Onkalo, who explains, “Nuclear waste that has to be treated so it doesn’t harm anybody and you can’t make nuclear waste go away.” In a word, the treatment is time: the waste must be stored until its poison fades. This must be done below ground because, as senior manager Timo Seppälä adds, “You just can’t guarantee stable conditions above ground.”

As Äikäs puts it, “There is no way of doing nothing.” Even aside from natural catastrophes, like earthquakes and storms, the surface is threatened by wars or other forms of aggression. There have been two World Wars during the last 100 years, the film notes (one 1000th of the time the waste needs to cool). And yet, Onkalo is built—in multiple layers, “like a Russian doll”—so it can function without human intercession or maintenance. Berit Lundquist. Science Editor of Nuclear Fuel and Waste Management in Sweden, says, “We shouldn’t have to guard it in the future. It should just be able to be left.”

All it needs is to be forgotten and undisturbed, essentially forever. It’s a “permanent solution,” but again, the very ideas of forever and permanence are only more complicated the more you ponder it.

The film evokes this complexity in images that are at once haunting and propulsive. Though the interviews are conducted separately, they are assembled to suggest a conversation, or at least a transition between thoughts. Even more affecting, the camera glides through the Onkalo tunnels under construction, sometimes narrated (again, for you as well as the future viewer, “Please turn around and never come back, there is nothing here for you, go no further”) and sometimes beneath the not-so-soothing sounds of Kraftwerk’s “Radioactivity.”

The rhythms of such camera movement aren’t lulling so alarming, and yet the film insists on the importance of forgetting, of turning time inside out. “How is it possible to create oblivion and forgetting?” Madsen asks. “How to make a facility like Onkalo disappear?” His experts can’t answer that. His film can’t show it. And so you’re left to wonder.