[syntaxers]

another way, If you are lazy to use outside applications, is to create a really dense plane. (like 200 length and width subdivisions) then right click the plane and convert to editable mesh. Enable soft selection and pick a few random vertices and move them up or down. Keep on doing this and you will end up with some funky terrain. Since soft selection is mathmatically based and does not look very "realistic" you can then add a noise modifier and select fractal and set the Z-power to make the terrain "rough"