With photoshop- we can use a mysterious imaginary city. Let’s see how..

Open your canvas  and drag a landscape imag.

pull out the Burn Tool (O) and use it to darken some areas to create some shadow.

drag in the cityscape image, resize it, and position it, make opacity 30%.

If buildings are not covering whole ladscape image, duplicate layer. flip it and place to fill.

create a new layer and apply the image: Image > Apply Image.

On this new layer, take out the Burn Tool again and darken the areas where the buildings meet the hilltops to create a smoother transition and in the sky area surrounding the buildings.

Get some stars and planet brushes and apply to the sky.

create a new layer and apply the image again (Image > Apply Image).

Now we are going to add some lighting to this layer, so go to Filter > Render > Lighting Effects and select 2 0′Clock Spotlight. Play about with the angling settings until you get something that you like.

Make another new layer and apply the image yet again.

go to Image > Adjustments > Color Balance.

Select the Midtones radio button and in the three Color Levels boxes,

enter these values: +46 +11 +13.

Now select the Highlights radio button and enter these values: +26 +16 -7.

Again, you can play around with these settings if you want a different look.

click on the half black, half white circle on the bottom of the layers palette and from the menu select Gradient Map.

In the dialogue box, select the Purple > Orange gradient which should be a default one and click ok.

Set this layer to soft light and lower the Opacity to 50%.

Do the same again but this time select a Black > White gradient map.

Set this to Darken and lower the Opacity to 20%.

Create another new layer and apply the image again. Go to Filter > Blur > Gaussian Blur, drag the slider to around 1.0 and hit Enter. I then set this layer to soft light at 20%.

play around with the depth of the image using curves

click on the half black, half white circle on the bottom of the layers palette and from the menu click on Curves.

From the Preset list, select Custom. Now play around with the curves for each RGB color in the Channels list.

we will sharpen the image, so go to Filter > Sharpen > Sharpen. Lower the Opacity of this layer to 30%.

Credit: http://psd.tutsplus.com/