Our current cities are comprised of enclosed, distant and introverted architecture equally isolated from urban life and ecological context. How might we open these spaces? How might we introduce pockets of space capable of triggering social encounters, multiplying circulation and facilitating the introduction of flora and fauna? This book gathers the research conducted by The Why Factory into what we term 'urban porosity'. Using both analogue and digital approaches, our researchers and students explored modes to open up our cities. What might be imagined to open our towers and city blocks? Stepped floors? Public stairways? Grottos in which city dwellers might meet? Could we manipulate building envelopes in order to increase façade area? Might we perforate built volumes and thus create pocket parks? Each of our hypotheses led to a series of step-by-step interventions that materialized in the form of a vast collection of towers built by our students using LEGO blocks. When gathered together, the resulting army of LEGO towers shows how far we can "and cannot" go. How much can a tower bend before it collapses? At what point does a porous tower become financially impossible to build or maintain?