Physical inactivity is a risk factor for numerous chronic diseases, and a mounting global health problem. It is likely that the outdoor physical environment, together with social environmental factors, has a tendency to either promote or discourage physical activity, not least in cities and other urban areas. However, the evidence base on this is sparse, making it hard to identify the best policy interventions to make, at the local or city level. This study seeks to assess the impact of one such intervention, the Connswater Community Greenway CCG), in Belfast, in Northern Ireland, UK. To do that it uses innovative methodologies, ‘Walk-along’ and ‘Cycle-along’ that involve wearable sensors and video footages, to improve our understanding of the impact of the CCG on local residents. The findings suggest that four characteristics of the CCG affect people’s activity and the benefits that the CCG created. These are physical factors, social factors, policy factors and individual factors. Each of these has many elements, with different impacts on different people using the greenway.