INTO ETERNITY "Dammit. Is this the hallway that goes into eternity or the one that goes to the rec room?"

"WE CALL IT 'Onkalo.' Onkalo means 'hiding place,'" director/narrator Michael Madsen gravely informs us at the beginning of Into Eternity. Well, he doesn't inform us, really—throughout his documentary, Madsen's voiceover is directed at those who might watch his film in the distant future. Like, 100,000 years from now.

That's how long the Onkalo nuclear waste repository will need to last before its contents are no longer lethal. Conceived as a remote place to hold Finland's nuclear waste, work began on the massive subterranean complex in 2004, where twisting caverns are even now being carved out of the bedrock beneath Olkiluoto Island. With a projected depth of over 500 meters, the labyrinthine, artificial cave will be so vast that it won't be truly finished until the 22nd century. "Onkalo must last 100,000 years," Madsen says. "Nothing built by man has lasted even a 10th of that timespan."

While Madsen's got a flair for the melodramatic—and while his occasional onscreen presence is utterly unnecessary—he's also got a sense for gripping imagery and an eerie, haunting tone. Little actually happens here, but it's fascinating all the same: We see the passages of Onkalo being slowly tunneled out, and we listen as parade of talking heads—officials, scientists, radiologists, laborers—talk about the practical and philosophical repercussions of their task. It's a massive undertaking, but the scope is even bigger: The experts argue over whether it's better to try to warn away whatever kind of residents Earth might have in 100,000 years—a task not unlike Neanderthals trying to communicate with us—or if Onkalo should simply be sealed and abandoned, hopefully being forgotten and never discovered.

While Madsen takes himself, and his film, very seriously—he somehow makes even a shot of a moose shitting in the woods seem pretentious—this subject matter is ominous, harrowing, and strange. This is a documentary in which it's clear that humans know very little about the present—mostly, just that we've gotten quite good at poisoning not only ourselves, but also our children—and even less about the future.