Quote - "The castle is maybe too much."

Yes, you are totally right. The image would look more realistic without the castle but it's against my nature to make just an empty mountain... :-)
I changed the color of the castle now, I think it integrates better with the surroundings.

Quote - "How dit you get the erosion?"

That's one GeoControl2 terrain. The erosion is a mix of "thin flows deep" and "thin flows sediment" (both with strength 50, starting point 5). I used the selectors of both erosions as a material distribution map in Vue.