Over the course of six weeks, add on. 20 höhenmeter transformed Vienna’s Wallensteinplatz into a hub of architectonic and artistic interaction: a temporary installation interacting with the public was erected in the summer of 2005 as usable object in the middle of a public square. As accessible environment, add on welcomed the exploration of extraordinary worlds and facilitated disconcerting perspectives and vistas. Differentiated perceptions of everyday needs and living spaces emerged, also of the location itself—a public space as stage and grandstand for real encounters. With this publication, Peter Fattinger,Veronika Orso, and Michael Rieper document the project add on through a comprehensive selection of images as well as episodes on the program. Essays by Reinhard Braun, Elke Krasny, and Roland Schöny negotiate the intervention in the ambivalent realm between publicness and privateness.