One of the latter is the current exhibition at Piccadilly Circus station.
Called Gold Card Adventures, and is a series of postcard images of places that the artist Ellie Harrison would have visited if the total length of her tube journeys for a year had been somewhere other than across the metropolis. As her site says:
ALL OF THE LONDON TRANSPORT JOURNEYS ELLIE MADE IN A ONE YEAR PERIOD WERE RECORDED. A CUMULATIVE DISTANCE OF 9236.6 KILOMETRES WAS TRAVELLED - THE EQUIVALENT OF TRAVELLING FROM EALING TO SHANGHAI!