https://i.imgur.com/kR2mi7e.png

An idea for the underground tunnels could be shading them in the right colour, one that feels good for something underground, then having a small legend on the map indicating what that colour means; i.e tunnels. Wouldn't take up much space either, a nice spot would be just below the North arrow.

Another that might work is making the lines indicating the tunnel walls dotted or much thinner than the walls of buildings above ground. Maybe both? A legend could be used to show this too, but I have a feeling the thinner lines would work intuitively. Them being thinner hints underground to me somehow, it might work haha.

Tank for Charlie position? Name for Hobbit could be valley since it's kinda closed in along there.

Corral for Radio room?

I like the little red rings for showing interactive spots! Cool thing to add to the other maps later on :)

My thinking was that the underground areas are the most important to understand, and that's why I made them the almost the same as a building.
Finding a path above ground to get from A to B is easy enough since there are pretty much no buildings to worry about, but the underground are effectively the buildings which need navigation.

Shading the tunnels their own individual colour could definitely work though, I like it.