How to make underground areas for terrain

I've read some other questions on this and I see that the ability to create underground areas for terrain currently requires modeling the terrain with another tool and importing it, or using a mesh object and doing a lot of work.

Is it possible to "poke a hole" in the terrain? What I mean is, to define that some grid region of the terrain heightmap won't have poly's or collision mask info. Then I could place a modeled cave entrance of some kind over the hole with a collision mask. This could be an entrance to a completely modeled underground. I wouldn't expect the terrain editor to support tools to create the underground, just allow turning off parts of the map and I'd take care of the rest.

If this isn't possible now, can you please consider it for future feature?

Thanks,

Greg Kourupes

I am not familiar with this poke-through but I guess you could hack something together with masking out a portion of the rendering and having triggers which disable collision temporarily. That said, I haven't used Unitys terrain that much. I just ran into trouble with it all the time and besides I haven't been creating games that make use of a terrain.

Sounds you don't want to use a height map but a voxel map instead. There isn't built-in support for this in Unity3D but you can look for existing extensions or create your own.