Not Exactly the most pleasant smelling place, but it's frequented by humans and feral-alike; it's one of the few means of transportation in the city aside from cars, or the city bus. It'd be in your best interest to be careful, and not to linger on the tracks - trains still shooth through these darkened, dreary tunnels at remarkable and lethal speeds. At night, the place becomes eery, and it's not a good idea to be caught alone here, for it is said that it's a favored place for the rougher types to hang out.
