Hey, not quite sure where you want to go technology wise, but I could image a large hydroponics lab which spans all the levels(except the secret one of course). My thought here is a number of central cores. Imagine something like a grain silo with plants growing inward with stairs on the interior and a central column between the stairs acting as the source for photosynthesis.

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So using a the crappy above ASCII art, the central part would be hollow space with a spiral staircase for gathering purpose as well as a perhaps half meter column to use for growth lighting in the center of the stairway. Of course, this lighting would have to be turned down when harvesting(or you get a quick suntan....lol) Nutrients for the plants would come from reclamated waste water and as the run off water flows down the shaft it is again recycled from the bottom(drainage) to be re-used multiple times. I got this idea mostly from some show or magazine a number of years ago that was talking about using the outside of skyscrapers to grow food. The original idea behind which was to reduce pollution caused by shipping of produce as well as something about temperature controls inside the buildings(don't quite remember, but I think the idea was that the plants acted as a form of insulation for the building.)