A func_wall is a very strange entity. It's basically a wall that can be triggered into or out of existance. id used func_walls on a number of levels to make a wall disappear and let creatures out to surprise you. If you have played single player quake any then you know what I'm talking about. Well they are real easy to use. Func_walls that is.
First thing you do is make the wall. Then you turn it into a func_wall. Currently this wall will not show up in your level. It must be triggered to work. So give the func_wall a targetname and create some sort of trigger like a func_botton or whatever and set the target of the trigger to the func_wall. So lets say you give your func_wall a targetname of wall1. Then you make a trigger_once to trigger it open. You would give the trigger_one a target of wall1. Now whenever the player comes in contact with this trigger_once then the wall will suddenly blink into existance killing anything blocking it. Cool huh?
There are a few spawnflags that you can set that will change the actions of the wall. They are trigger_spawn, toggle, and start_on. Trigger_spawn must be set if you have triggered the func_wall. In all the possible uses that I can think of for the wall I can't think of one in which you wouldn't have trigger_spawn set. start_on makes the wall work in reverse. Instead of the wall blinking into existance it will blink out of existance. This is how id uses func_wall in a lot of their levels to let monsters out of a secret room to surprise the player. If start_on is set then toggle must be set also. I actually don't think it has to be set but if you don't set it then you will get a error message when entering your level. Probably a bug in the code but it doesn't hurt anything.
Thats all there is to a func_wall. On the [example
.map] there are 2 examples of uses of the func_wall entity.
One of them is a kind of weird trap. Where the player goes for
a weapon and suddenly walls come up all around him. So check
it out! As always if you have any questions, tips, or comments
then please post it on the discussion board.