hey, @takehara!
Good job on this one, it looks super solid! I like all the details you did to design this gate too!
You could also try to apply some atmospheric perspective to this piece to make it even more "in-depth". Perhaps around the bottom of the image where the pillars are to exaggerate the fact of how up high the whole thing is located.
I touched up your piece roughly to show you what i mean.
Basically the saturation decreases with distance.