From your description, you meant for the arch to be a passage to another world?



I think the arch needs to be defined a bit more or the terrain to be a bit more sporadic from one plane to the next. The mountains seem to flow into each other even though they're not directly flowing through the arch. The only thing that defines the other world is the color of the sky. Maybe make the arch look a bit more alien; more high tech, an aura around it, electricity pulsating off of it?



I think that would really help with the effect you want.



But this is very nice, I like it!