Public space can create social memory and enliven cities through the use of constructed spatial elements, streets and squares, as well as through the spatial events and interventions that take place in these particular spaces. With the help of these elements, urban space becomes its own open-air exhibition. People from all walks of life can create an ongoing communicative relationship with the space and with the city. Today, a new design culture is stimulating production, action and interaction. Multiple and elusive meanings, a pluralistic environment and the participation of the audience in design are emphasised. In the discipline of art and architecture we are moving from static, definite and finished icons to more open, changing and reflective spatial entities. New forms of art and new architectural installations in urban spaces provide an experimental medium for citizens to communicate with their surroundings. They can re-structure their spatial perceptions and reconceptualise the spatial structure of the city. By disturbing usual everyday practices, rhythms and choreographies, these new art forms propose alternative living scenarios in public space. It is these creative spatial interventions that enliven both the body and the city. Resonating with the work of Shelley Smith, Nicolai Steinø, Ana Carolina Lima e Ferreira and Katerina Mojanchevska in this volume, the aim of this chapter is to discuss the contributions of participant and audience-oriented art and architectural installations to urban public space. Selected installations are examined in terms of their spatial potential, their ways of transforming public space and the tactics that are used for the redefinition and recreation process. It is believed that decoding the design features of these sophisticated installations will enhance our spatial awareness and help both designers and architects to create more such innovative concepts and, in the process, encourage the re-definition of public space.