Geograph - photograph every grid square

Mark Wallinger, one of the UK’s leading contemporary artists, has created a major new artwork for London Underground to celebrate its 150th anniversary. The result, commissioned by Art on the Underground, is a multi-part work on a huge scale that will be installed in every one of the Tube’s 270 stations.

Mansion House is a London Underground station in the City of London which takes its name from the nearby Mansion House. It opened in 1871 as the eastern terminus of the Metropolitan District Railway. Today, Mansion House is served by the Circle and District lines. It is between Blackfriars and Cannon Street stations and it is in fare zone 1. The station is located at the junction of Queen Victoria Street and Cannon Street.
Mansion House is a sub-surface station with three platforms. The westbound platform, number 1, and the eastbound platform, number 3, are shared by both the Circle and District lines

The London Underground system is also known as the "Tube". It is the oldest underground system in the world, the first section dating from 1863. The present system has over 250 miles of track and 272 stations. There are 11 lines covering Greater London, Essex, Buckinghamshire & Hertfordshire. Nearly half the system is above ground.
Wikipedia: Link
Transport for London: Link

A few years ago I read a book by Mark Mason "Walking the lines" in which he walked the route of the London Underground lines, overground. I will repeat this visiting all 272 stations (some more than once). My route tries to follow the line of the railway as closely as possible, using footpaths and roads, deviations are made to make the walk more "interesting".