Minecraft wiki entry for Building_a_metropolis, associated text: Invisible City: Make everything in your city made of glass blocks, glass panes, barriers, and/or ice, with no doors for your buildings. However, leave the ground grass, snow, or whatever block it already is. Building an invisible city is pretty risky though, as you can't use any lights, so monsters can spawn in your city. Because of this, it's best to build this city in Peaceful mode, or use the /gamerule doDaylightCycle false command to make it always day.