Sewer

A sewer was a cavernous tunnel and pipe system through which effluent and excess storm water flowed away from the inhabitants of a city.

The Sixth Doctor and Peri investigated the London sewers on at least two occasions (DW: Attack of the Cybermen; DWAN: Time Wake), while the Tenth Doctor and Martha were chased through the sewers of New York City by Daleks and pig slaves. (DW: Daleks in Manhattan) Weevils lived in the sewers of Cardiff. (TW: Combat and others)