Doesnt make much sense, I see maps just as long. Without any interference. Should I put a brush of a wall behind my sky texture.. Maybe it will show that?

Ive made a map, thats pretty long. But there seems to be a problem, if you are in-game, and you look out, you see the sky, and not the other side, I tried taking a weapon with a scope to see if that would help and it kind of didnt. Seeing to the other side is sort of important in this map. I just need to know how I could possibly fix it.