SKIES

Ok, there has been speculation on how these are done properly so let's set the record straight. Whatever you do DON'T in-case your whole map in a box covered in the sky texture, this will cause your whole level to be drawn by VIS and therefore cause it to slow down and lag like crazy on any server. So here are some images to give you an idea:

All that has happened here is I made the buildings and then copied them up somewhat and applied the sky texture to them, once this was done I put a huge brush over the top to act as the ceiling. Make sure you apply the sky texture to all sides of the brush.

Don't forget to add a light_environment in there as well, this will light the whole map for you.

And to change the sky texture you have to go to the MAP menu at the top of the editor and click map properties. Then you can edit the sky in the cl_skyname box.

The skies that come with HL are as follows:

2desert
alien1
alien2
alien3
black
city
cliffe
desert
dusk
morning
neb1
neb6
neb7
night
space
xen10
xen8
xen9

As you can see, the engine helpfully makes the sky look seamless in game.

By blink-(1)(8)(2)