With the growing ability to capture information about cities and their constituents, designers and technologists have the unprecedented opportunity to understand, improve, and invent spatial dynamics. This chapter focuses on the Underworlds project developed by laboratories at the Massachusetts Institute of Technology in collaboration with the Kuwait government. It combines robotics, bioengineering, and genomics to paint a microbial portrait of the urban environment. The bespoke network of automatic samplers works in the sewage to collect data about health trends at a high spatial and temporal resolution, which gives researchers tools to analyse many facets of urban dwelling and public health. At the same time, with mounting public concerns over data privacy, smart-city endeavours such as Underworlds are facing a critical juncture in their evolution. With a sensible eye toward how these endeavours respond to and evolve with the blurring boundaries between public and private, cities and their citizens can collectively harness the boundless opportunities smart cities promise.