Trying to generate a structure when game starts

I am making a 2d sandbox game and when the layer spawns I want to generat a kind of broken down castle. How would I go about doing that in a generated world.

Well @cherno My question is how would I go about spawning a generated structure into a world that is newly generated every time you make a new game.

Just build it before the game starts…

Why does it need to be on runtime?