If you want to create a path that is raised a little from the surroundings. create a terrain with the path you want to take with the airbrush in the terrain editor. Then click "Erode". "Lower" the terrain and I recommend using "Gaussian Edges" to make sure your path doesn't disappear sharply but gradually if need be. Add weeds at the edges or bushes for a little crafty concealment if neccessary. You can inverse the whole terrain for a sunken, worn path and do a negative boolean operation like Nu-Be suggested. Just an idea to help. It works very well for doing railroad trackbed ballast.