Urban sprawl has a strong impact on the provision and use of green spaces and, consequently, on the benefits that society can derive from these natural ecosystems, especially in terms of public health. In looking at the Sustainable Development Goals and other regional policy frameworks, there is a strong need for quantifying access to green spaces. This study presents and applies a methodology to model the physical accessibility at national and sub-national scales to public green spaces (i.e., urban green spaces and forests) in Switzerland, using AccessMod, a Digital Public Good (DPG), and ArcGIS travel time functions. The aim of this study is therefore to establish the physical accessibility of public green spaces by modelling access to both forests and urban green spaces at the national and sub-national scales of Switzerland.