Garry's Mod Horror maps aren't exactly regarded to high standard... and for good reasons. Source is a difficult engine to get a hold of and I'm not just talking about Hammer. This results on most horror maps being almost entirely recycled to the point that if the most basic change to the formula ganders high praise, even if it is not entirely deserved.

There are a few things that I'd like to note that people should AVOID when making horror maps:

• Mazes. Don't get me wrong, mazes can enhance a horror map, but, as they are most frequently implemented... mazes are inserted into a map solely to put more jumpscares or make the map feel longer. They are unneeded if that's what you're using them for.
  
• Obnoxious jumpscares with zero to no buildup. You can make the jumpscare as loud, as grimy, as unexpected and as high quality (visually) as you want, this won't make them any better. A png jumpscare with good buildup and clever sound usage is not only scarier but also feels much less onoxious than an out of nowhere ghoul that screams real loud. It's all about the aftertaste, one could say.
  
• Boring and uninteresting environment. What's wrong, love? You haven't touched your 54th horror map that takes place in a boring abandoned dark concrete building. If you do not make the location visually interesting or unique, the player will most likely will get bored before they reach even the halfway point of your map. The worst offenders of this include: Generic abandoned concrete buildings, Generic wooden manors, Basements, Schools, Slender forests, Evil laboratories and of course The Backrooms. What I would love to see is more unique locations for a horror scenario, like a submarine, a residental complexes, an Industrial factory, a cargo ship, a plane, an airport, an underwater facility, a space station, an alien planet, Local villages, Caves, Non-abandoned buildings, Offices, No Man's Land, etc. Something, anything to keep the player interested. A good horror game isn't just scary, it is interesting to immerse yourself in. If the player isn't scared, they just won't play the map further.
  
• Combat. Fighting zombies isn't scary by itself. Make it feel scary.
  
• Puzzles. Don't get me wrong, puzzles can enhance the horror map when done right... if done wrong, however, will do the exact opposite. Offenders include Shape Puzzles and Jigsaw puzzles. The kind of puzzles that stagnate the whole map at best and ruin the atmosphere at worst.
  
• Huge spaces or Agoraphobia. This is commonly found of "first map" type of horror maps, where the mappers only recently learned how to use Hammer. So, unless you're using these open spaces to enhance the horror, they don't add anything to the map and only make it slightly more annoying to play.
  
• Obnoxiously loud sounds. Last thing I want to get when playing video games is tinnitus.
  
• Confusing layouts. If the player spends most time questioning where they need to go or what to do than actually playing the map, it becomes not only less scary but also frustrating.

The most important thing is for the map to be fun and interesting above all else. Yes, even above horror.

With that out of the way, let me introduce you to my personal collection of GMOD Horror maps. I found these worthy of being called "good" horror maps. And they should be held as an example on how TO make a good horror map, in my opinion, of course.
I do have to clarify that while I think these maps are good, they are not perfect. Most have at least 1 or 2 flaws that I have mentioned before, but the positives outweigh the negatives.

Note: I will not be adding following horror maps into this collection no matter how good they are for one reason or another:

1. Joke "horror" maps. Some of them are quite fun and hilarious, but, they're not really horror maps.
   
2. Co-op horror maps. While I do have friends, I do not wish to pester them about my niche interests in gmod spooky maps. Also, friends just make any horror map barely scary, in my experience, no matter what.
   
3. Horror "exploration" maps. While some of these are certainly scary and interesting, I do not include them as they deviate a bit too much from what most people would consider to be a "Gmod horror map". Maybe I'll make a seperate collectiong just for them, we'll see.
   
4. Horror TTT/Murder/Etc. maps. Same as above.

Feel free to suggest maps that you think deserve the spotlight in the comments.

I am looking for a horror map that I am unable to find anymore and I'd like to put it in this collection as it was a very good horror map and I would appreciate if anyone would help me with finding it! It was a map that took place in a desert crypt, of sorts. Players have to go through multiple sections of the crypt to do some sort of objective on each section to unlock the main door. One section even had a spirit that you had to avoid. The ending I precisely remember player being strapped to a chair until a monster or something approached them.
Again, would be really grateful if someone would help with finding it!

Edit: Thanks for 4 stars! Didn't think it would get that far, huh? Again, thanks a lot, this collection was made of love for the community and not of hatred. Have a spectacular day!

Edit2 [10.07.25]: This collection isn't abandoned, there just weren't many good horror maps that have been released in the past year.

Edit3 [07.09.25]: 5 STARS?!?!? Wow. Thank you all so so much!!! And, again, the collection isn't abandoned, as soon as I find a good horror map, I'll make sure to add right here! Or maybe I'll make a new collection, idk. I have edited the collection slightly to be a bit more presentable. Thank y'all so much <3.