Blackfen is not blessed with an extensive sewer system and most of the waste of everyday city life ends up on the streets, attracting vermin and causing disease and illness, as well as a terrible stench. The sewer system that does exist is exclusive to Old Palisade Town and primarily serves the wealthy. The streets where the buildings are connected to the sewers are generally much cleaner and the air much less nauseating. Although the council is periodically pertitioned for the sewage to be expanded to further parts of the city, neither the desire nor funds are available for such work.
The sewer system is fed by an underwater stream and is primarily made up of channels of water which wash the waste into Black Lake. Since the lake is large and the sewage system relatively minor, this is mostly washed away. The sewer itself is well constructed, being made of hundreds of stone blocks and heavy supports.
While many of the channels are too narrow for any but the smallest to get through (and this would be extremely unpleasant as they are filled with the waste being washed into the lake) some are far more generous in their proportions, including some intersections which are almost vast chambers. Alongside the sewage channels of these larger areas many also have small raised stone paths which run along the side. These were put here so that workers could gain access to various parts of the sewer, without having to wade through the putrid water.
Of course, one of the consequences of having created this network of sewer paths is that the criminal gangs of Blackfen - and in particular, the South Blackfen Boys - use it to pass undetected under the city, as well as storing goods there and to distribute their wares undected. Such is the extent of this activity that the South Blackfen Boys have undertaken a massive operation of reworking many of the tunnels and have now constructed a large network of tunnels that they use to aid their criminal activities, many of which are entiely unknown to the authorities.
The majority of these tunnels, which are very poorly constructed out of wood, are well hidden from the main sewers, through which access is gained. They are just tunnels and do not serve the sewage system in any way, and are prone to collapse. They are also prone to being flooded by the sewers during periods of heavy rain, when large sections have been known to collapse. Dotted around this network of tunnels are many chambers and rooms where goods are stored and gang members hide.