create hole in terrain -- pass through terrain/transparent terrain

I’m trying to figure out how to create a ‘hole’ in unity terrain, with the end result being a cave entrance.

The cave itself will be a mesh creation, but i want to be able to create a hole in the terrain to let the player pass to the mesh which would be positioned under the terrain, and also see through the terrain into the cave mesh beneath.

I’m not sure if this is possible at all… But i figure i’ll ask

Heres a script to how to make the player pass through the terrain:

However, the transparent part of the terrain is probably going to require another shader.
May I recommend the free Microsplat: MicroSplat | Terrain | Unity Asset Store

And it’s terrain hole plugin: MicroSplat - Terrain Holes | Terrain | Unity Asset Store