Because we still can't digging caves in to the terrain (reliefs)...
Will be cool to have some scaled cover reliefs for tunnels or underground buildings.
For the moment we must use rocks to can we them cover it.
We need something like in photo no. 3 as example.

For me personally carving in the terrain isn't that all important to me. As I plan to use the same methodology the Bethesda team uses for caves. Their terrain system is no different than Game Guru's at present. Caves are generally engineered by use of cave parts as an interior space. Also large rock cave entities for if you wish to make them outdoor. Technically you don't use the actual terrain plain for this.

Basically you'd have an entrance to a cave that loads a new map of an interior space of caves.

However in your picture examples it looks like your looking for the ability to easily have a tunnel go through the terrain, not an entire cave level. So I can see your problem there. Wonder what Lee may come up with to sort these types of situations?

EDIT: I just did a test last night using an interior caving system, with the B snapping tool and it actually worked out very well. I personally was able to make an okay caving system with just objects and snapping them together. Only problem is there was no way to change the perspective in the editor to really make the map look unique with the tunnel objects. Also I wasn't able to go any higher than 1 story. It was just a bit too tedious with the limited tools.

Solved "Hidden buildings under terrain" (underground buildings) with terrain cover assets.
I've been imported all the assets of "Terrainpack" folder from the old FPSC.
You just change (add) the scale options and set the "materialindex = 0" to hear grasses sounds.
Also, I've used "NoTerrain()" plus "NoWater()" for increase at 120-140 fps game frames.
In this video appear smaller fps's because the "Fraps" screen recorder program use a lot of video resource too.



See in the attached photos the real speed (fps) without "Fraps" program.

Good work Old Larry!

Thanks Teabone. With that "goindoors.lua" script the number of polygons decreased from 299700 to 96000.
The terrain use too much resources in the game. In my opinion the maps must be smaller not that huge.
See in the photo below how much of the map surface I've used (Less than a quarter of map surface, and the polygons used is still huge).
P.S. In the photo you only see the bottom right of the entire map I've used.