Hanging Gardens of Rock City, 1970

Photo collage, touched with green crayon, by Liliane Lijn, who 'imagined a utopia of green walkways across the rooftops of Manhattan'.

Found at the British Museum, see a larger version here.

Update: Thanks to reader Martha for letting me know that this is part of a series by Lijn, and can be seen on her website, which is full of interesting work.