Ah, there's the joy of it: 1500 lines of code defines "a grid point", and then when you create your map, you instantiate however many gridpoints with the properties you want. If I understand what dragonchild means, a gridpoint is probably smaller than a room, having properties such as opacity, density, and the like (that is, you can or cannot see or move through it in certain directions).

While I am not (by any means) experienced in D&D matters, I would love to join up to try to make that kind of a 3D world system workable.