Minecraft wiki entry for Nomadic_experience, associated text: This design protects you from mobs even if you build the shelter at midnight. You should stay careful when going out of it, as a mob may fall into your hole. If there are any mobs on top of your hole, you might not be able to sleep due to them being too close. If you do not place a torch inside to light the shelter, it will be dark enough for a mob to spawn.