The sociology of knowledge that followed The Social Construction of Reality shifted from the study of rarified ideas to practical activity, focusing on the stabilization of a sense of shared reality. The opposite side of this shift in emphasis has received much less attention – activities that place reality into a state of play and, in so doing, call attention to its ephemerality. I discuss three empirical areas where the practical use of other realities is central to the sociology of knowledge. First, I document cases in which skilled practitioners, such as airline pilots, safety engineers, and athletes, use simulation to prepare for events that are understood as highly uncertain and risky. Next, I describe how other realities are mobilized epistemologically, such as through experimentation in technoscience and experimentalism in unrealized or ‘unbuilt’ art and architecture. Finally, I consider autotelic and transcendent social experiences through fantasy and technological mediations like augmented realities.