DownSights writes “Black Ops Cold War: Zombies’ first map, Die Maschine, has not disappointed when when it comes to how much content it offers, including the main easter egg and side easter eggs.
In this guide, we have covered each step required to complete the main easter egg on the Die Maschine map. This guide is optimized to ensure you complete your final boss fight at the earliest round possible. We managed to get to the final boss fight by round 17. You may be able to get into the fight even at 15-16, depending on your resources.”
Source: N4G PC Full Solo Die Maschine Main Easter Egg Guide (Megaton Orlov) – Cold War Zombies