I recently had an LD in which I was able to change my terrain, and thought it might be a nice technique to share with you guys. First of all, my reason for trying to change the environment was that it was very hectic in my current location, and I wanted a nice field or clearing in which to meditate peacefully (to get down to business with my subconscious).

However, rather than thinking "Terrain! Be a meadow!", I simply mentally constructed the terrain behind a nearby hill. I imagined a field behind it, and after walking over the little bump of a hill, there was my field (I actually did this again, because in the first little field, I could still see & hear the excitement I was trying to leave).

My theory as to why this works is because I find it very hard to refute things I "know" in a dream, whether I know I'm going to be spotted by enemy spies or I know my living room is next to my dining room. In this case, I already knew what the terrain around me was, and couldn't change it, because I could quite obviously see what it was. However, I did not know the terrain behind the hill, and so, my mind was quite suggestible as to what might lie behind it.

Anyway, hope it helps.

Cheers,
RobotGymnast