It's a free performance piece by Fitzrovia Noir running from Wednesday
24 July to Saturday 27 July, from 10am-11.30pm and 12.30pm-2pm, with 4pm
matinees on Wednesday and Friday.
"By ‘picking up’ passengers on this people-powered train along the way, the artist-driver will establish imaginary overground routes through public spaces with an innovation that responds to 150 years of underground travel in the capital." says the blurb for the event.
No booking is required, so if the weather's dry (cardboard trains don't run well in downpours) it should be an interesting experience.