Glass

Glass in Quake is a transparent barrier that is often contained in a frame. This barrier is featured in the level RealGlass - from The QuakeLab. Unlike a normal wall, Monsters can see through a wall of Glass.

Glass is designed to exist as an impenetrable wall, intended to be seen through but not allowing any entity to pass through it. It is possible to destroy Glass, whereby the Glass will simply disappear and entities will be allowed access to the opposite side. However, due to the extremely large amount of health that Glass possesses, it can be extremely time consuming to destroy one of these walls.

Shub-Niggurath, also not intended to be killed by normal means, has far less health than a pane of Glass has. Without modifications in the editor, it would take multiple lifetimes (several millennium) to destroy this barrier.