Minecraft wiki entry for Mushroom_farming, associated text: Another way involves making the farming area just one block high and paving any walkways with slabs and using a water system to channel the mushrooms out of the farm room and into a collection point. This removes most of the danger since mobs cannot spawn on half-blocks or in one-block-tall areas and any other areas can be lit up. The Nether is a safe place to start a mushroom farm since mobs there will not spawn in small spaces.