London sewers

The London sewers were a series of tunnels beneath the city of London on Earth.

Throughout the 19th and 20th century they were used by a variety of species, usually not for their intended purposes. In 1889 they were used as a base of operations by Magnus Greel who populated areas around his base with large rats. (DW: The Talons of Weng-Chiang) In the 20th century, the Cybermen utilised the sewers to travel throughout London prior to their (failed) attempt to invade Earth with Tobias Vaughn's assistance, the used the sewers once more in the 1985 when they were attempting to alter their own history. (DW: The Invasion, Attack of the Cybermen)