Now, we'd better cage the player in a bit. In my opinion, one of the most important decisions in building a map is how to block the borders of the map without making the player feel like they are trapped or living in a box; this can make all the difference in how realistic the map feels. The best borders are those that are layered, for example a vehicle, followed by a fence, followed further back by a small building and finally by the far off mountains in the skybox. Some of the Raven Shield campaign maps go to great lengths to make you feel like you're part of a larger world. When I burst through the Garage level for the first time, and found myself looking at a 3d modeled ocean, I fell out of my chair.

With all that said, we'll be keeping it pretty simple for this tutorial. Our goal is simply to keep the player from ever seeing a 'horizon' where the ground abruptly ends and the sky begins. Not only does this look unrealistic, but if the player peeks over the edge, they'll see a hall of mirrors effect. That doesn't mean you've built the skybox incorrectly. You just need to do a good job of keeping the player away from the edges.

Create a cube builder brush sized Height=224,Width=16,Breadth=1408. In the texture browser, open "Airport_T.utx", choose "Wall" and select any of the wall textures. Add one wall on the far side of the world and one wall on the near side, right along each edge. Next, place a shorter wall (sized Height=64,Width=736,Breadth=16) to block the left edge of the map. However, then place an identical wall about 256 units in from the first one to keep the player from getting to close and peeking over the edge. Our 'sun' won't do a very good job of lighting these, so open up their surface properties, select the "Unlit" checkbox, and click the "Apply" button for each one. (I rarely recommend using the "unlit" setting in a final map, but it'll do fine for now.)