This paper takes up the notion of ‘unbuilding’ as a critical lens for analysing how urban worlds are made and unmade. As a counterpoint to demolition, construction and repair, unbuilding reorients attention to temporal disjunctures, material agency, and contested futures. Here, the intentionality of design is both implicated in, and challenged by, unruly materials, violent unmakings, and subterranean extractions. Grounded in research on the afterlives of high-rise housing in London and Nairobi, and part of an ongoing collaborative conversation, the paper traces some of the material, political, and ecological possibilities of thinking about cities through unbuilding.