Teufelsberg, the devil's mountain, is an artificial hill in the south-west of Berlin that looks out over the city. A leisure park much used by young Berliners, it was built after the Second World War from the rubble of the bombed city: the mass of debris piled there is estimated at thirty million cubic metres, the equivalent of four hundred thousand buildings. The hill rises on the site of a building that was never finished, and the work follows what grew on top of that buried history.