Before I begin my explanation of the guide and tips for this map, I would like to say this is a very high-quality map. The feel of the map reminds me of Grosten Haus from WWII, and here's to say I loved that map. This map has only one minor bug that I have found, which I have showcased below, however I don't believe it is particularly game-breaking as it is extraordinarily rare and only occurs out of the window to the left of Quick Revive.

You can also flush the toilet on the first floor bathroom. I am not entirely sure what this does, but it is something you can do by pressing "F" on it.

Some candles will also ignite when going near them. I do not think this has any effect either.

There are four Teddy Bear locations which if all activated by pressing "F" on them, will do something possibly? I did not notice any changes (including music).

1. Directly right of Quick Revive
   
2. Through the 500 point door from the spawn room (bathroom)
   
3. In the fireplace in the Double Tap room
   
4. In the corner of the second-story bathroom, directly left of Juggernog

There are five challenges, and one final "challenge" that unlocks once the other four are completed. Each of these, once completed, give a different reward.

Locations & Challenges

1. Left of Quick Revive: "Complete all challenges and return."
   
2. Left of Speed Cola in the kitchen: "Survive 20 rounds."
   
3. Connecting room to Double Tap: "Get 300 headshots."
   
4. Middle of the Double Tap room: "Get 50500 points."
   
5. In the second-story hallway outside of the bathroom: "Obtain 4 perks."
   
6. Behind the main stairs on the second floor: "Get 500 kills."

Rewards

1. Buyable Ending
   
2. Stamin-Up
   
3. Deadshot Daquiri
   
4. Widow's Wine
   
5. Mule Kick
   
6. Electric Cherry

For maximum efficiency, you can restart until you spawn with the RATT handgun. I have found it is a one-shot headshot until at least round 15, resumably much farther with Double Tap. This will help you get 300 headshots quickly.

I have found that I personally could stay in the spawn room until round 9 with the Gewehr 43 (G-43). Once round 9 hits, more perks are necessary to continue surviving, notably Speed Cola.

This is a tight map with very few pheasable survival places, however the most effective I have found is in the Double Tap room, watching the two windows and training around the center pole. Stay to the sides of the room and slide through zombie hordes, but don't stick too close to the side to avoid getting suck on level geometry.

Since there is no PAP, wonder weapons and LMGs are absolutely necessary. Personally, my favorite loadout is the MG-42 and Wunderwaffe DG-2. The Wunderwaffe gets you out of a pinch and the MG-42 mows zombies down without a hitch.

If you manage to no-down, you should be able to complete the map on round 20. A typical game will be round 23-26 however. I'm very curious to see what the highest-round is, but I was able to get to 24 before ending.

So concludes my guide on this amazing map. It is small and there is enough content for half an hour to an hour of fun. I will update this guide if I or anyone else finds any other Easter Eggs or any other effects I didn't notice.