In the second half of the twentieth century, American readers of Arthur Conan Doyle’s Sherlock Holmes stories – known as Sherlockians – worked together to create a ‘world of Sherlock Holmes’ that crossed the boundary between reality and fiction. This book applies an innovative literary-geographical lens, informed both by geographical theories of spatiality as a process and literary scholarship readers’ active roles in making stories happen, to define the contours of a world in which the ontological boundary ordinarily assumed between the actual and the fictional bend, blur and break. Drawing extensively on the University of Minnesota’s Sherlock Holmes Collections, the world’s largest archive of Sherlockiana, this book aims to shine light on Sherlockian activities in the mid- to late-twentieth century. This is a relatively understudied but creatively rich period, in which the imaginative foundations of the fandom as we know it were laid. In these years, the world of Sherlock Holmes was collectively created by readers through a variety of textual and embodied practices: writing, mapping, playing and walking.