Participants in a subtlemob
are invited to a specific time/location where they listen to a prerecorded soundtrack, a mix of music, story and instructions. Like a being in a spontaneous film with no cameras and no certainty of whom else is taking part...
In a similar, although more playful, vein is Improv Everywhere
. We especially like their no trousers on the tube stunt. subtlemob Improv Everywhere