Source image used and two of my own images - bridge and dog.
I first opened all three images.
On the grass image, I split the channels to RGB to find the best one to select the background.

I selected the background (split channel) with my magic wand and saved the selection to an alpha channel. I went to the original grass and loaded the alpha channel and pressed delete.

I then copied and pasted as a new layer my bridge photo and inverted the selection and pressed delete. I cloned areas of the water to fix where the subject's hair was.

I softened the edges of both layers where they meet.

I then went to my dog photo and erased the area around him, selected him and pasted him to the grass/bridge scene as a new layer. I brought his brightness down a bit, duplicated him for a shadow and brought the lightness all the way down for the duplicated. I added a gaussion blur to the duplicated and aranged it where I thought the shadow would go.

Here is the bridge pic - subject removed.

Here is the dog pic - subject removed.

I added a new layer. I used my paintbrush at a low opacity with no hardness using white and put a "glow" in for the moon. Then brought the opacity up some and hardness up some and added the circle for the moon.

I added a new layer and filled it with a semi-transparent gradient.

I zoomed in real close, toggles the gradient view so I could see the bridge better and started coloring on a new layer. My brushes changed a lot - the hardness and opacity. I colored the main part yellow and orange (as it is at night) and then with the hardness and opacity very low, I put dots of different colors on the bridge. I put a very slight gaussion blur to this layer. I then went over the dots with a little harder brush with the opactiy up a bit. As you can see, it just isn't lit up enough though.

I added another layer and added a 1 pixel bright white dot to each light to make them stand out more. Here is what it looks like with the colored layer toggle off--just white lights. Kinda neat.