Architecture and social behavior might appear to occupy different worlds: one the physical world, the other the social world. Yet for many animals these two worlds are intimately connected, having reciprocally shaped one another over ecological and evolutionary time. The connection between architecture and animal social behavior is perhaps nowhere more intimate than among social hermit crabs (Coenobita compressus), which have evolved to occupy architecturally remodeled shells and which must navigate a shell housing market requiring substantial social interaction with conspecifics. Here I review over a decade of experimental work on this system. I focus on the dynamic feedback between behavior and architecture, particularly the ways that behavior shapes architecture and the ways that architecture in turn shapes behavior. I highlight the fundamental importance of studying physical mechanisms of behavior, which in the social hermit crab system has involved fusing experiments on social behavior with detailed analyses of shell architecture, often through interdisciplinary collaborations with engineers, morphologists, and biomechanists. Altogether, these studies have incorporated diverse approaches that span field and laboratory, and underscore the significance of studying architecture to fully understand the evolution of social life. Based on these long-term studies of social (‘so-shell’) life in social hermit crabs, I conclude with a broader conceptual framework, which outlines the scope for studying dynamic feedbacks between architecture and animal social behavior across a wide variety of systems. With this approach, scientists can ultimately deduce general principles of how and why architecture shapes social behavior and vice versa.