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 at least twice. (TV: Attack of the Cybermen, PROSE: Time Wake)

The Fourth Doctor and Leela encountered giant rats in the sewers of Victorian London. (TV: The Talons of Weng-Chiang)

The Tenth Doctor and Martha were chased through the sewers of New York City by Daleks and pig slaves. (TV: Daleks in Manhattan)

Weevils lived in the sewers of Cardiff. (TV: Combat and others)