Masked the image. I used a very sharp edge for the tower itself and a softer edge for the land at the base.

Next I made 3 copies of the masked layer. Then I used the warp tool on the bottom most layer.

I repeated this for the middle masked layer.

I then sandwiched a copy of the moon stock image between the previous two layers

Then I turn on the top most copy of the masked tower layer and gave it a slight warp.

Then I made a space scape for the background. There are a lot of tutorials floating around out there on the web. I've included a link at the beginning to 31 different ones. Take your pick. For this one, I started with a black filled layer, copied it. Added 10% noise to the copy (Gaussian + Monochromatic). Duplicated this layer and changed the blend mode of the duplicated layer to Linear Dodge. On top of this, I used a large soft brush with a blue color to make the wispy clouds. The opacity and fill were set to about 20%and 30% respectively. For the brighter, sparkly star a used a lens flare on a black layer above all of this and set the blend mode to screen.

Duplicated the moon's layer and set the blend mode to multiply to darken it's mood a little. Then gave the towers in front of the moon some shadows.

It did not make sense to me for the two towers on either side to have windows on their sides. So I cloned them out.

A few more tweeks to the tower shadows.