I think in order to remove damage done during the. I then built what i wanted inside the terrain. I then framed around the terrain with rebar concrete as its outside borders, except for the very top edges, which i covered with terrain and then set the prefab to 'allow topsoil decorations' in Pilles editor.
What I did was to create a map with terrain that matched what i wanted in the prefab so that it would look natural, I chopped the entire piece out and exported it as a prefab. We can also make pillars of dirt, gravel, stone etc. They can make big holes like volcanos and tunnels.
Adjust the land up and down with these two tools.
