UFF is an interactive audiovisual installation which documents the action of 18 artistic interventions in the public places in Prague on 19.5. 2009. The installation enables to watch a video documentation of the performance via interface which runs particular actions on the map of the city. UFF is designed to be a simulation of a dialog between the city and its inhabitans. Are we passive or active inhabitans? Do we have a chance to regulate the rules of the "game" within the system? UFF is a kind of engaged geocaching with elements of street-art. A game as an active form of cognition, space perception, creative approach in solving problems and answering questions.