Minecraft wiki entry for Nether_survival, associated text: You do not want to have your mines where you are farming mobs. More spawn in your mines and less spawn where you are farming. To prevent this, know where your main hub mining system is in proportion to your base. You need to make sure all of your biomes where you are farming things are outside of your mines. For example, if your base is at X point, and all of your biomes where you farm mobs are south of your base, then your mining tunnels must go north in proportion to your base. That means that your main hub mining tunnel must go between east and west, with the seperate mining tunnels going north, in that specific example.