Cloned and patched the inside of the light bulb to make it appear empty. Cut, pasted, flipped, distorted etc etc the insides of the bulb to create the building blocks of a "city". Then positioned them in the bulb, blurring some to create an out of focus look in the "distance" and "foreground".

Started creating a background, brushed in some grey at the base, then used either a "pattern overlay" in layer styles, or a filter (sad to say I can't actually remember which!). Then rasterised it and used "smudge" to create random stalagmite type shapes.

Brushed, blurred, dodged and burned some layers on top to make it look atmospheric.

Copied the light bulb city a few times, changing the actual city components a bit so they dont look identical. Positioned behind where the main pic will be, with various amounts of gausian blurring.

Positione the main pic in the centre, faintly erased part of the upper left curve so you can see another bulb through it. Oh, also by this point had overlayed the screw fitting of the other bulb source over the silhouette of this one, using "hard light" at 33% opacity, so it looks in tune with the rest of the pic.

One of the last things I did, was to create a little elevator on the outside of one of the buildings, using one of the "building blocks" made smaller, and smudged, then added 2 little lights - I think this is almost too small to see, except in the high res.