Reality Factory

I have a couple questions on brush geometry. 1.) I've been working on a level that needs an area with a "fake" wall that the player can walk through. 2.) there are places in the level that I don't want the player going into, but I still want it to be visible. Any help is appreciated.

create the wall out of different sections, have one wall either side of the gap, but dont use a cut brush.
then fill the hole in with another wall and flag this one as empty, if memory servs me correctly it should still render but is now able to walk through.

2.) Place a solid brush as a barrier and mark it as "Clip" brush in the attributes dialog. This will make the brush invisible ingame but the actors will still collide with it.

've been working on a level that needs an area with a "fake" wall that the player can walk through

Make it a model of a Liquid entity and give the Liquid
the resistance of air.