Placing "Cut" objects?

Hi there! (First post on here, so please be gentle with any criticism’s)

I was wondering if anyone had any idea on how to add(Place) objects whilst in-game such as buildings, that actually cut into the terrain(So make a hole rather than just distorting), so if I were to build say a bunker whilst in-game I would be able to walk into it and then walk underground?

(Sorry if its unclear, if you let me know what you find wrong I will try my best to explain in better detail.)

The terrain system in Unity does no support true “holes” because of how the terrain is created. In order achieve what you are talking about you would need to either develop your own terrain system or purchase an existing system that is available. I have heard good things about this system: TerraVol but have never tried it myself.