How to set thickness to terrain plane

very simple question and can’t seem to find this anywhere, the terrains in unity are a simple plane, is there a way to, for example, instead of a plane use a cube or a parallelepiped, and the top surface of that object would be the terrain where we can edit elevations and details?

Not exactly sure what your trying to do, But if you make a cube plane it HAS to be set as “terrain” in order for you to set its properties (thickness etc.).

You can’t. You can use other objects and meshes for a Terrain and give thickness to them. But unfortunately you cannot set the thickness of an actual terrion. The thickness is always fixed. What are you trying to do, maybe there is a way around.