Deep within the bedrock in western Finland, flashing lights from heavy machinery cast shadows in eerie tunnels that lead to a tomb that must remain unperturbed for millennia.

There is a reason the catacomb on the lush island of Olkiluoto was buried 400 meters below ground: It will house the world's first spent nuclear fuel disposal facility.

The project, which aims to solve the age-old quagmire of what to do with nuclear waste, is nearing completion in a region that is already home to Europe's largest nuclear reactor.