Designing Active Cities focuses on improvements to the built environment that will promote active lifestyles and healthy habits. Active Cities make physical activity a priority by transforming the urban environment into spaces that encourage activity for the urban population. Providing the opportunity to move, play and interact are ways that urban design and architecture can ensure the built environment is supporting active living. Active City design has become a relevant topic across Canada following research from the board of health that identifies Canadians to be increasingly inactive due to their surrounding environments. The relationship between the built environment and active living is mutually dependent, where improvements to the population's activity levels depends on improvements to the city's urban fabric. This thesis explores how design can address inactivity in the city and contribute to improving the population's activity levels through interActive Plug-ins that transform the urban fabric of Toronto, Ontario.