Archivo: Why London Underground is nicknamed The Tube

Description: The nickname "Tube" comes from the almost circular tube-like tunnels through which the small profile trains travel. This photograph shows a southbound Northern Line train travelling to Kennington via Charing Cross leaving a tunnel mouth just north of Hendon Central station.
Title: Why London Underground is nicknamed The Tube
Credit: Own work
Author: SPSmiler
Permission: I, the copyright holder of this work, release this work into the public domain. This applies worldwide. In some countries this may not be legally possible; if so: I grant anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.
Usage Terms: Public domain
License: Public domain
Attribution Required?: No