Hammer skybox?

So i go into my map and it looks all messed like this: http://prntscr.com/6nxpc5

In hammer it looks like this: http://prntscr.com/6nxon0

How do you fix?

You don’t have a skybox around your map.

How do i make this?

Well for now I’d just suggest making a hollow block around your map, at least while you’re still building it. So select the tools/toolsskybox texture, drag a block around the entire boundary of your map, and hit enter. Then go into the Tools tab, click “Make Hollow” and set a value of -32. Obviously, once your map is finalized, you can delete this skybox and build a better one, but for now a hollowed cube should do.

Think of your map as a submarine, and brushes are the walls. You want to make the map completely sealed or your map will “leak”.

If your map leaks you’ll have quite a few issues.

You can seal it with any brush. If you want a skybox, apply the material tools/toolsskybox to it, and it will render the skybox on that face.