This paper explores the creation of fictional space in participatory design and relates the notion of fictional space to the more general conception of design space as a space created through the situated practices of participants. The notion of fictional space provides insights for understanding the process through which participants in participatory design create a design space in which established conventions of everyday practice are altered or suspended. With inspiration from literary theory, it is argued that the production of fictional space may be understood in terms of participants practicing games of make-believe mediated by props. The motivation for discussing fictional space is traced through ongoing work on designing new exhibition spaces for museums. Through a case study from a participatory design session, it is explored how games of make-believe progress and the role of props in this process.