The GeoE3 project, co-financed by the Connecting Europe Facility of the European Union and involving the National Land Survey of Finland, established a lightweight yet powerful data integration platform to demonstrate how national geospatial services can achieve European-wide interoperability. Starting from existing national services, the project transformed them using new OGC APIs and mapped the data to a unified INSPIRE specification, creating a harmonised framework capable of supporting complex use cases like building energy efficiency analysis and smart city solutions. Alongside the core platform, GeoE3 developed supportive tools: an e-learning platform (Location Innovation Academy GeoE3) to guide national mapping and cadastral agencies (NMCAs) and businesses, an interoperability map to illustrate how well data aligns across borders, and a data quality dashboard to visualise data consistency and reliability.