I did my writing for the day and as I'm off work decided to play with the Net - never a good thing to do.
I happened across and old piece of free software called Terragen, and after stumbling around for a few hours came up with this.
I could get hooked. The only thing is, as it's free, it doesn't include any models for me to play with- no trees or forests, rivers and that kind of thing. Nevertheless, I think I'll have to delete it if I ever want to get any more writing done ever again.