CERN, renowned for operating the world's largest particle accelerator, also manages the world's largest computing grid, the Worldwide Large Hadron Collider Computing Grid (WLCG), which spans 170 institutes across 42 countries and supports immense data processing needs. To monitor this vast infrastructure, CERN utilizes Grafana and Grafana Mimir, tools that provide crucial visualization and alerting functions, allowing the organization to handle diverse data sources efficiently. Grafana serves as CERN's primary monitoring interface, with over 5,000 users creating thousands of dashboards, while Grafana Mimir addresses the challenges of integrating long-term storage for Prometheus metrics, proving scalable and flexible for their extensive operations. CERN's deployment includes both public and private instances, ensuring accessibility and security, and Mimir's integration has enhanced their data handling capabilities, allowing for significant scaling and multi-tenancy. Looking ahead, CERN is considering additional open-source tools like Open Telemetry and Grafana Tempo to further enhance their monitoring capabilities, highlighting the foundational role Grafana plays in their infrastructure.