Well, I got my idea I think; it's a project about vertical layers of a city with a splash of surreal-ism.
This will be a vertical cutaway (with some perspective of course):
Essentially the top layer will be a city scape with different scales of buildings and simple natural elements. I won't go too crazy with it, there will be stairs such as fire escapes and going into buildings, then prominently in the scene, a subway staircase will lead down into the subway. From the subway, a maintenance shaft will have stairs leading down into the sewers (which will will be kind of romanticized with stone and exposed water. Water will even pass from the street level behind the subway into the sewers. From there, a small water level beneath the sewers will go in-front of the stairs going down into the next level which will be scaffolding type stairs of varying quality leading down into a slight labyrinth of a shanty town (I was going to do an idea similar to this with last month's but didn't have time and now this month is far more appropriate) sort of a 'world below). It will have an eclectic look to it with lights and pipes all over.
I know that's a big block of text, but there's a lot to go into it, the stairs will basically act as vertical stitches throughout the cutaway.