Cities and urban planning are crucial for a sustainable future. However, challenges such as urban sprawl, limited data, and methodological issues hinder effective monitoring of urban green spaces (UGS). UGS are essential for enhancing liveability, public health, and climate resilience, yet rapid urbanization threatens their accessibility and equitable distribution. Hereafter, we present a reproducible, scalable, and open data-based approach to assess accessibility to UGSs in support of SDG 11.7, which calls for universal access to safe, inclusive, and accessible green and public spaces. Building on the data-information-knowledge-wisdom (DIKW) framework and FAIR principles, we implemented, within the ESA-EU Horizon 2020 GEOSS Platform Plus (GPP) project, a web-based service integrating two open-source tools inAccessMod and AccessMod for automated data preparation, travel-time modelling, and accessibility estimation. The resulting indicator provides estimates of the share of urban populations lacking access to green spaces within defined walking distances, enabling comparison across cities and possibly monitoring over time. Results demonstrate the feasibility of generating harmonized, reproducible knowledge products that could ultimately support science-based decision-making and climate adaptation. Despite current limitations in datasets and simplified travel scenarios, the proposed approach provides a cost-effective, replicable, and possibly policy-relevant solution for global UGS monitoring.