A vast reservoir of information on human health and behavior lives in our sewage. And this resource is untapped. At MIT SENSEable City Lab they imagine a future in which sewage is mined for real-time information that can inform policy makers, health practitioners, designers, and researchers alike. Such is the idea behind Underworlds: a cross-disciplinary, open-data platform for monitoring urban health patterns, shaping more inclusive public health strategies, and pushing the boundaries of urban epidemiology. Early warnings in relation to the presence of new flu strains in urban centers could significantly reduce a community’s medical costs and even help mitigate outbreaks. In addition, smart sewage could impact the way non-communicable diseases are studied, because biomarkers for diseases such as obesity and diabetes can be measured at unprecedented scale and temporal resolution.