Hello again fellow cartographers!

I finally got around and sketched a rough layout for a cave map I had planned for a few weeks now.
The whole thing goes quite deep and is enormous (the biggest room measuring several kilometers in length).
It's set in a fantasy-world and inhabited by a subterranean species, that's partly intelligent. (you want more detail? ask xD It's not relevant for the map though)

Anyway back to the map itself:

I would love to convert the whole map into an isometric view but I'm not sure how to work with all those floors when I want it all to be on one map.
Another problem is the size. As mentioned: It is huge, including whole cities at several points. I'm not sure how to convey that size to the viewer? Would that be necessary at all? (I'm bad with math and numbers xD so I'm not very good with scales).

Other than that I'm open for any kinds of critique.

Here's the sketch:
Click image for larger version.  Name: CaveMapWIP.png  Views: 99  Size: 860.0 KB  ID: 93014