This article discusses the issue of approaching the design of the ubiquitous city as a matter of topology. The general context here is the design of contemporary global urbanity in the form of u-cities, smart cities, or intelligent cities emerging with the second phase of network societies that increasingly develop mixed reality environments with context-aware out-of-the-box computing as well as the soci-ocultural and experiental horizon of a virtually and physically mobile citizenry. Design here must meet an ongoing and exceedingly complex interactivity among environmental, technical, social and personal multiplicities of urban nodes on the move. This chapter focuses on the design of a busy traffic intersection in the South Korean u-city Songdo. Hence, the discussion whether and how Songdo may be approached via design as topology primarily considers the situation, event, and experience in which multiplicities of environmental, technical, and human interactants tend towards gathering and dispersing in a single mixed reality street transport scenario. The need for ‘intelligent’ ad hoc connection, routing, and disconnection of multitudes of humans, technical systems, and environmental entities makes this scenario one of the more crucial design test beds. This article offers a critically comparative discussion of a variety of ontological and epistemological approaches to design as topology, including realist, nominalist, and constructivist efforts in both cultural theory and technical studies. It is demonstrated that design as topology offers significant resources with respect to traits of the u-city such as continuous material and energetic flows, its environmental landscaping of mixed realities, its ongoing virtual and physical infrastructural developments, the folding and unfolding of its architecture, its nodal dynamics, and the relational mobilities at stake. However, this chapter also questions design as topology as an approach when it comes to decisive aspects of urban finitude: citizens’ lived experiences, concretization of urban information and communication technology ICT, and sustainability.