In Michel Foucault's body of work, the notion of heterotopia stands out as both particularly intriguing and particularly underdeveloped. Introduced in the introduction of The Order of Things (first published 1966) and further described in the lecture “Of Other Spaces” (1967), heterotopia has been used by scholars in a variety of fields, from social theory to architecture. Of special interest is the way Foucault describes the relationship between heterotopia and utopia, one defined by its liminal nature and the other by its unreality. This work seeks to shed new light on that relationship, by focusing on heterotopias as threshold spaces between the real social world and the perfected but unreal world to come. I approach the concept of utopia with an eye toward its eliminationist implications, and use three extermination camps established as part of the Nazi regime’s Operation Reinhard as cases through which to explore significant features of a heterotopia, how those features manifest in these cases, and what connects these spaces to the world that can be glimpsed in the mirror they create. Although I primarily use historical cases as a way to expand existing theory, I aim to build upon that expansion by pointing the way toward the development of new theoretical tools for historical-comparative analysis of spaces of both extermination and detention. Finally, I suggest that work might be done focusing on embodied identities as themselves forms of heterotopia, which introduces possibilities for additional analysis of the roles of bodies and identity in cases of certain kinds of mass violence and death.