The interconnected system of land, food, energy, water, and climate, known as the Nexus, requires integrated management for efficient and sustainable resource use. Barriers to achieving resource efficiency in Europe include policy inconsistencies, knowledge gaps, and technology lock-ins. The SIM4NEXUS project aims to address these challenges by developing innovative methodologies, including complexity science approaches, a Geoplatform for data integration, a Knowledge Elicitation Engine for strategy integration, and a web-based Serious Game for immersive decision-making experiences.