Background: Our living environment impacts on our health and wellbeing. The physical and mental benefits of interaction with nature and the ecosystem are well-established in literature. From a public health perspective, it is thus crucial that people make use of public green spaces (PGSs) in urban areas. Therefore, it is important to understand why they are potentially under-used.Methods: In this research, we identified social barriers that prevent the (full) use of PGSs in the Brussels Capital Region (BCR). We applied a qualitative research methodology. Insights were generated through 51 individual face-to-face in-depth interviews with a group of PGS users diversified in terms of age, gender, migration background, and socioeconomic situation. Questions were open-ended, and the interview guide was semi-structured.Results: Our research identified three social barriers for the use of available and accessible PGSs: (1) perceived dangers due to bad precedents, the presence of socially frightening elements, or a lack of social control, (2) not feeling in place because of the dominance of a specific group of users or because of community perceptions, and (3) not fulfilling one's social needs. These barriers were different in their manifestations (barriers to go—barriers to stay—barriers for integral use) and resulted in a differential degree of PSG-use. We distinguished three different dimensions of the completeness or integrality (understood as full or optimal use) by which PGSs are used; the spatial integrality (using all the different parts of the PGS), the temporal integrality (using PGSs at all moments of the day), and the social integrality of PGS use (without any restriction concerning social interaction).Conclusions: While there are many benefits associated with PGSs, a continuous social evaluation of these physical places might generate social barriers resulting in a decline of their use, a more superficial use, or even in complete avoidance. Both the social context and social needs of individuals result in specific social barriers.