Being physically active in natural environments has been linked with multiple mental and physical health benefits. However, not all urban contexts can provide their residents the same access to green areas for walking and sport activities. Mediterranean cities provide open spaces for physical activity that differ from those of Northern European cities. This study explores both conventional spaces in the form of public parks and urban green spaces, i. e. beaches, tree-lined streets, boulevards and public squares, in relation to the daily walking levels of residents in a Mediterranean city, such as Barcelona by presenting findings based on examining and assessing spatio-temporal exposure levels measured with the help of smartphones and publicly available GIS layers. To achieve this, both exposure and daily walking time were measured from GIS and GPS-based smartphone tracking data for 127 adult individuals from Barcelona, Spain. Based on these measurements, it was determined that the presence of large-scale open spaces for physical activity, such as beaches or large parks in the participants' daily walking routes, proved to have the highest association with daily walking time. Also, underexplored forms of nature, such as street trees were also positively correlated with individual walking levels. Additionally, small-scale public spaces, such as public squares and boulevards, indicated a considerably negative association with walking time. The findings from this study confirm existing evidence on the health benefits of urban greenness and broaden the analytical focus on the role and impact of green space provision on physical health. Altogether, street trees and the presence of both blue and traditional green spaces proved to be significant factors of increased walking levels.