Eager to jump into Nazi Zombies on PS3? You'll need to finish the campaign first—it's not a bug, it's by design. Treyarch made Zombies a reward for completing the story, and there's no legitimate shortcut around it.
The campaign serves as an extended tutorial. It teaches movement, aiming, weapon handling, and—crucially—the perk system that Zombies builds upon. Skipping it leaves you unprepared for the mode's escalating difficulty.
World at War's campaign is widely considered one of CoD's best—gritty, atmospheric, with memorable missions like "Vendetta" and "Heart of the Reich." It takes 6-8 hours on normal difficulty. That's a single weekend for permanent Zombies access.
Pro tip: Play on Hardened or Veteran for a real challenge. The skills you develop—ammo conservation, flanking, cover usage—transfer directly to high-round Zombies strategies.
Bottom line: Play the campaign. It's good, it's not that long, and it unlocks Zombies the way the developers intended. No risks, no bans, just pure gameplay.