Public open spaces play an important role in promoting physical activity (PA). This study aimed to describe user characteristics of public open spaces (POSs) given the type of location and levels of PA. The study also evaluated the relationship between the environmental determinants of POSs and PA intensity. The study used observational data to measure environmental determinants and obtain information on users and their activity levels in the POSs of Darab in Iran. Out of 13,342 individuals observed, the proportion of men was slightly higher than that of women. More than half of the users observed in the community parks performed vigorous activities. Children and teenagers were found more often than other age groups doing vigorous activities. Most of the observed users performed vigorous activities in the evening and sedentary activities during weekends. Seniors were more sedentary than the other groups. Greater size, and better facilities and aesthetics of POSs increased the odds of being more active. However, a higher number of incivilities was associated with a greater chance of walking and lower odds of performing vigorous activities. As the quality of POSs contributes to PA levels, stakeholders should consider the quality of such spaces to improve retrofitting and designing POSs to maximize activity levels.