Artist Colleen has been out and about with her magnet. Go to her blog to see her other projects.
Here's what she had to say:
"I've been walking round for the last few weeks with a little magnet. You have to find something to stick the magnet to when you uncover your beauteous treasure and snap it.
Old favourites appeared. I looked out of my bedroom window at a Hawksmoor Church for years (before the recent prettifying by English Heritage) so no surprise perhaps that the shabbiness of St Alfege's in Greenwich should attract the magnet.
The delicate elegance of the legs of one of the donkeys posing on Blackheath probably captured my imagination because of London Fashion week. Or maybe the fact that I have always fancied an alternative career as the owner of a fleet of donkeys on a sandy beach.
There's homage too to John's mission to beautify schools across the borough, the detritus from plane trees notwithstanding, with his dry gardens.
And just one of thousands of modest little gardens, this one tucked away at the foot of a block of flats near the Regents Canal, hemmed in by a rusty fence and filled with lovely green hellebores.
There's plenty more beauty in the city. The problem now is I've lost my magnet .'