The sufficient provision of urban open spaces (UOS) is fundamental for sustaining good quality of life in cities. This is an aspect long established within urban planning. Indeed, the balance between built masses and open spaces has been crucial for the discipline’s development and innovative practices in spatial design. This paper presents a pilot study correlating the concentrations of built form and population with 10-minute walk access to UOS, including both grey and green areas. We realise this in three steps. First, we verify the availability of all UOS for flexible utilisation by the public. Second, all UOS are evaluated through a qualitative score matrix. And third, we assess the amount of UOS that is accessible from each residential building within the 10-minute isochrone through network analysis. The research results challenge the notion that citizens in denser neighbourhoods have poorer provisions of good quality UOS. On the contrary, the examined case studies illustrate that inhabitants within denser areas have physical access to a greater quantity of UOS. This fact becomes even more significant when one considers the individual open spaces’ elements, amenities and connectivity. The realised analysis indicates that if one aims to effectively assess the provisions of UOS within cities, a more complex and diverse picture must be drawn in the evaluation process. Only then the impact of planning strategies such as urban densification can be fairly evaluated with respect to the pressure the process puts on the available green and grey UOS.