Looking For "Realistic" Cavern Maps

[Nytmare]

So I've been digging around, looking for inspiration for a prop map. The style I was hoping to find was a bird's eye view of a large cavern network that wasn't the stereotypical, two dimensional, flat D&D map, where it's a bunch of hallways with rocky walls. I'm not even sure if what I'm hoping to find even exists.

I was hoping for some kind of established shorthand, that in some way described three dimensions (but without contour lines), with levels and caverns overlapping each other, without having to show the entire cavern in a three axis, perspective drawing, or as a 2D horizontal cutaway. (mostly because my map is going to be miles to a side)

Has anyone ever seen anything like this?

My current plan, if I can't find someone elses' style to steal for myself, is to do it with the passages following a general grey scale where high things are white and get darker as they go deeper. Then I can do drop shadows under the overlapping bits to bring out that third dimension.

Man, I'm picky...