- "Sometimes the best plan is to lock the doors and wait until morning."
- — Mission Briefing
Gröesten Haus (German for Biggest House) is a Nazi Zombies survival map in Call of Duty: WWII. The map itself is essentially a co-op version of the Prologue, being situated only within the farmhouse. It is unlocked once the player has either completed either version of the main easter egg on the map The Final Reich.
Like the solo version, the secret Mystery Box easter egg can be used to aid the player in their survival. However, this version of the map features a secret easter egg that isn't in the Prologue, which allows every weapon in the Mystery Box to be upgraded. In this version, there is also a special Blitz machine titled "Random Blitz" that can give the player a random Blitz perk, similarly to the Der Wunderfizz machine from Call of Duty: Black Ops II and Call of Duty: Black Ops III.
The map also features special enemies, in this case being the Wüstling, who will start to spawn on the map starting on wave 10 as opposed to the ones that spawn starting on wave 20 in the Prologue. On wave 50, the player will encounter a Brenner.
With the February 7th, 2018 patch, a new character, the Bloodraven Mountaineer, can be unlocked by completing three specific challenges on the map.
Players spawn on the bottom floor of the farmhouse in front of the front door. Directly in front of the players when they spawn is the MP-40 weapon locker, which can be obtained for 1000 Jolts. To the left of the player's spawn is one of two staircases that leads upstairs. To the right of the player's spawn are two door ways separated by a fireplace, the one on the left leading into the kitchen area while the one on the right branches off into a small side room that will bring the player into the kitchen as well. Within this side room is the map's only Geistchild machine and the STG44 weapon locker for 1500 Jolts. Within the kitchen is the other staircase that brings the player upstairs.
Coming from the kitchen staircase will bring the player to an area of the upstairs which contains the Combat Shotgun weapon locker for 1000 Jolts. To the left of the Combat Shotgun is a hallway that connects the two staircases. Within this area is the Random Blitz machine for 2000 Jolts and the secret Mystery Box room, which can be opened by shooting all ten lanterns throughout the map.
On May 29th, 2018, Gröesten Haus was released in Multiplayer as a full-on map with the release of the Attack of the Undead community event. In this rendition of the map, the map is opened up to allow for more gameplay, featuring a whole new exterior area alongside the normal farmhouse. It is available in Infected, Hordepoint, and Relic of the Undead. A 24/7 playlist was also added, allowing the map to be played on Team Deathmatch, Domination, Kill Confirmed, and Hardpoint.