I love this bit! It is very simple, but messy, and amazingly fun. It will transform the model into a realistic scene.

There are a number of ways to approach landscaping, and I guess it does not really matter how you go about it, as long as the end result pleases you. I start by building the hills etc up with anything I can find. Polystyrene packaging blocks are ideal. (remember where your additional features will go: roads etc). After you are happy with the basic shape, I would cover them in strips of newspaper or packing paper) wet with wallpaper paste, and allowed to dry. I the bought a 25Kg pack of Plaster of Paris. This mixed to a runny paste and used to saturate any material (old towels etc). Get everything ready before you mix. Once it starts to go off, you get very little time, and you cannot do anything else with your hands covered with plaster. Oh, and cover the rails with something: the plaster is hard to remove after it has dripped on the rails.

 Obviously, fields will be flatter than I produced here.