I'm not reffering to scale, I'm talking about ....like a wall with a dent in it.
and this is like I said vertical..along z.

Okay, this is a different thing.
In this case, you would have to use models. You can always combine terrain, which has the advantage of faster rendering with models. And in MED you can easily convert terrain into model and also the other way around (as long as the model has a "regular" grid).