Modeling hole in ground?

[Damascus]

Are there any resources I could use to model something for free? For my first mission, all I want to do is change the outside/zimmarman_ground Static Object so that there is a hole in the ground hear to the top of the slope. I can't think of any other realistic way to simulate a hole/crater blown in the ground.

Maybe I'm being a little too ambitious for my first mission, though. The introduction to my mission is for the player to be hiking outside (possibly on a mountainside) when he finds the entrance to a buried dungeon.