I was told recently (by Nigel) that Hungarian architect Erno Goldfinger describes his craft as the ‘art of enclosing spaces’. The following two projects play, respectively, with the addition and removal of artefacts from public spaces.
add something
Play Me I’m Yours is a street art project in which pianos get left around the city for strangers to play. It’s quite charming and a great example of how very simple things can interrupt daily routine, bringing people together.

The picture above was taken in York by this chap.
Read more about the project here or see what the Guardian had to say about it.
take something away
The unconscious art of demolition is a collection of photographs showing the ‘scars’ buildings leave on their neighbours when they’re demolished.
The artist is Marcus Buck. More photos here. Hat tip (really?) to Kottke.

