It's an Art of Imagination. I used simple Pencil Shading. The wallpaper of a city on my computer inspired me to draw something like this. I made a City. But the area above and below the city was void.
I made a water body, an ocean and draw the shadow of the buildings. Now for the sky i draw dark clouds, and the shadow of clouds can be seen in the ocean. As the clouds cover the city, i named it City Under Clouds.