the Guardian's caption: Land-mark ... a cyclist passes Richard Long's artwork Box Hill Road River, in Surrey. Photograph: Brian Cleckner/National Trust
Richard Long's centre line on the zig-zag portion going up Box Hill in Surrey, part of the cycling track for the Olympics: evidently it was inspired by the graffiti chalked on the roads during the Tour de France, which, now that I've looked it up, isn't that interesting.
Here he is talking about laying down the road paint, like a thief in the night. an authorised thief in the night, with a team of helpers.