Okay, so I have a 3D array [12,12,12] how would I go about getting all the objects adjacent to a given object in the grid. I need this for the A* algorithm.

Nevermind I figured somthing out.

Watch out for edge of map endcases ......

Even more fun with 6 clip planes logic instead of 4 ......

12x12x12... just brute force it. When you get to around 10⁴ entries you might need to use a spatial decomposition for an efficient search (such as a nearest neighbour search on a k-d tree)... but for such a small matrix, brute force will always be faster, since you don't waste time building the decomposition (but lose time on the search).