The map shows only the largest passageways of the sewers. These are of two sorts - primary and secondary, according to size. Primary passages are 20 feet across and contain 3-foot-wide railless walkway ledges on both sides. Sewer workers cross passages by means of a their 16-foot "catch-poles" to vault across or by the use of boards, which they lay down as temporary bridges. The catch-poles are also used for reaching below water level to clear debris from sewer gratings. Secondary passages are 12 feet across with a single 3-foot-wide ledge on one side (usually the more southerl or easterly). The countless feeder pipes (and sewer pipe less than 1 foot in diameter) and tertiary tubes (which can be crawled through by a Medium or smaller creature) are not shown.
Junction rooms are usually 30-foot-by-30-foot stone cubicles, 20 feet high with a sitting ledge near the ceiling, above the muck. Surface shafts are 6 feet in diameter with iron rungs set in the walls to use as ladders to and from the sewers. The entrance to a shaft is a 3-foot-wide hole capped by a removable metal (or metal-banded wood) cover.
The accompanying map is accurate, but some of its features (such as the junction rooms and surface-shafts) are distorted in size for clarity. The sewers themselves are unnamed, so those giving directions usually give them in relation to the point of entry.