The Viennese architect Michael Wallraff's visions of urban planning represent a clear break from tried-and-true scenarios of horizontal city development.Wallraff has spent years delving deeply into both the use of vertical spaces in the city's fabric and ways of creating new dimensions of social interaction via prototypical open public spaces situated within densely populated urban structures.This first overview of his projects and ideas explains the central principles of Wallraff's experimental practice and simultaneously provides important impulses for the reinterpretation of urban density.