I've seen a few windows (particularly in space themed levels) where you can look outside and see other parts of the maps or roaming enemies. However, you can not shoot out these windows or walk through them. The level Acme Station is a good example of this, and so is Aye Mak Sicur or Morpfhine. The picture I've attached show the kinda window I'm talking about. I thought it would be simply be made by creating an "item impassable" polygon but upon inspecting the map in Weland, it seems as though this isn't the case. I apologize if this is a dumb question with an obvious answer but I can't seem to wrap my head around how to create these windows, I've even read all through the original Forge manual but couldn't find anything on this. Would appreciate some insight!
Creating a window you cannot shoot/jump through?
Double click the line that you want to be solid, and check solid. It's a condition of the line adjoining the polygons, not the polygon itself.