How do you make an invisible wall?

I will try to be quick.I am trying to make a cool window with a fence blocking it and i did everything,mainly looking into my favourite megawad community chest 3,map 06.But i can't get the wall behind the fence to be invisible so that i can see trough,i want to make an awesome outdoors area that is acessible from a locked door,my format is GZDoom:Doom 2 UDMF and here is what i tried:
-Setting the render style to translucent and changing alpha to 0
-Checking the Transparent box to see if it helps
-Setting command 208 with alpha 0

Split in 2 the sector of the window with a linedef. On this linedef put as middle texture your desired fence and set the linedef to be impassable.
Or are you trying to make a door which let you see through the other side?

Basically,a fence that works line a window and behind a invisible wall instead of a visible wall

Right click the line you want to be an invisible wall.
Check the "impassable" box.
Right click the line to be the invisible fence.
Add texture of your choice to the middle segments on both sides.

That should be all that's necessary.

If there are still problems check to make sure 2 sectors are not sneakily sitting on top of each other. Use the create sector mode and click around, that usually solves that issue.

Thnks,i will try making it like ya sais.The fence IS the window instead of just a Palace guarding it.Another question,how do i create a pillar that crises to the ceiling when you press use once you get a specific key?

Make the pillar sector and give it a tag, then use http://zdoom.org/wiki/Floor_RaiseToLowestCeiling action (or another floor-related action) with parameters of your choice, and assign the action to the key or switch that you want to trigger the action when grabbed or pressed.

I already did that,it as ed me the yellow key but when i got it nothing happened,i didn't tag anything,tough

*asked

> Didn't tag anything though

Well there's your problem. The simple way to fix that would just be to use a WR/W1 action, assign it to a nearby linedef, and use the handy dandy sector tag # to match up the linedef action and the sector you want to do the thing. What you're asking for is a bit more complicated, but this is a place to start.