For the Opera House project in 1998, the City of Linz had selected a “plot without a base area”. An area was designated between the Danube, the expressway and the steeply rising Schlossberg mountain, which made extensive construction underground, within the mountain and in the existing tunnel system necessary. We proposed a project located slightly off the designated building plot. As specified, the main volumes are located within the mountain. However, the essential interest in the project was to open up the ground volume and to technically reconstruct the surface thus destroyed. The project was an attempt to remodel the lost configuration of the surface. Paths and trails were turned into steel frameworks spanning more than 60 meters; the rock surface was traced using technical grids and transparent membranes.