Well to start, I think the perspective of the wall and the ground (where the water is) is a bit weird, plus the floor on the right seems to be leaning to the left for no particular reason. I think there could be a bit more work with the colors as well: they are a bit dull. The mountains need to be more present, not lost in the white clouds. Finally, the guy climbing the wall seems to be floating in the air. He looks like a stock you'd just copy paste on the wall.

Overall, the idea is nice. However, those are a few technical problems you need to fix. Consider the perspective mostly, since it's very wrong.

WOW!