/vr/ - Retro Games

So, the tutorials on mapping I've read were all for indoors maps. I want some outside maps too however. I know that the sky is generated by putting the F_SKY1 texture on the ceiling, but how about skyboxes? Pic related was a tutorial I found with a section on skies and it mentions how to create an actual skybox, but not how to show it. Does anyone have a link to a good/comprehensive outdoors mapping tutorial/skybox tutorial?

As for the specific thing I'm doing now, it's the level that segues into an outside. For the final bit of the level, you open the door that goes outside, and you see the "vast outside", but it's inaccessible. Scripted event happens that spawns two mancubi, you have to fight them, and once they're dead and you touch the door, the level is over. (Next map has you starting outside though, with closed door behind you).