Glass (InstanceTopic, 4)

From Compile Worlds

Glass is a brittle material, usually transparent, used primarily in windows.

In the world of Iji, glass is forbidden. Ceiling fixtures must be headbutted and windows must be kicked.

Glass is also available in Minecraft, where it is made by smelting sand, and once placed cannot be recovered (breaking glass gives nothing back to you). It's very useful as it lets you see what's out there without endangering yourself.