Add a fourth dimension to your model railroad—sound! Your trains are most likely already equipped with sounds, but have you thought about the sounds in your environment or background? Maybe it is the sound of a waterfall along a mountainous countryside, or the urban buzz of a cityscape. Many websites offer free sound files you can use for background sound. With the use of an inexpensive MP3 player hooked up to a speaker, you can enjoy an extra dimension while bringing your model railroad to life!