How to do it...

To paint and make use of a hole in a Terrain, follow these steps:

1. Open your copy of the Unity project from the previous recipe.
2. Add a Spot Light that shines on where the cube is sitting by going to Create | Light | Spot Light. In the Inspector window, set its Position to (0, 0.5, 0), its Range to 50, its Spot Angle to 125, and its Intensity to 2. This will allow this light to light up a bonus level we'll create beneath our Terrain.

3. Delete the cube from the scene – in a full game, this cube will be removed when a goal has been achieved, revealing the entrance to the bonus level we are going to create.
4. Select Terrain in the Hierarchy window.
5. In the Inspector window, select the Sculpt and Paint Terrain tool (the second icon, which looks like a paintbrush). 
6. From the drop-down menu in the Inspector window, immediately below the five terrain tool icons, select Paint Holes.
7. Select the first...