The ATLANTIS project aims to assess the technical and economic feasibility of transforming open-pit coal mines into hybrid energy storage projects. The envisaged repurposing of coal mines into hybrid pumped-hydro power storage (HPHS) sites for excess energy supports coal regions in transition according to the EU Green Deal, provides added economic value, stabilises regional job markets and contributes to the security of the EU energy supply. Industry partners from Greek and Polish energy industry contribute to the ATLANTIS objectives with their expertise and extensive data on the respective national energy economy and their open-pit coal mining regions, including ongoing renewable energy projects in the coal regions in transition.