Background: Evidence suggests that many contemporary urban environments do not support healthy lifestyle choices and are implicated in the obesity pandemic. Middlesbrough, in the North East of England is one such environment and a prime target for investigation. Methods: To measure physical activity (PA) levels in a sample of 28 adolescents (aged 11-14 years) and describe the environmental context of their activity and explore where they are most and least active over a seven-day period, accelerometry and Global Positioning System (GPS) technology were used. Twenty-five of these participants also took part in focus groups about their experiences and perceptions of PA engagement. Results: Findings indicated that all participants were relatively inactive throughout the observed period although bouts of moderate-vigorous physical activity (MVPA) were identified in four contexts: school, home, street, and rural/urban green spaces, with MVPA levels highest in the school setting. Providing access to local facilities and services (such as leisure centres) is not in itself sufficient to engage adolescents in MVPA. Conclusion: Factors influencing engagement in MVPA were identified within and across contexts, including ‘time’ as both a facilitator and barrier, perceptions of ‘gendered’ PA, and the social influences of peer groups and family members.