The paper introduces the COST ACTION "Underground Built Heritage as catalyser for Community Valorisation (Underground4value)" (2019-2023). The action aims at establishing and implementing an expert network to promote a balanced and sustainable conservation of the underground heritage, and realise its potential in urban and rural areas for regeneration policies. In particular, it investigates four case studies per year on underground regeneration policies, and provides knowledge on main technical and organisational barriers to the underground regeneration and correlated solutions, by also developing new training modules. The action advances, on the one side, in the classification of artificial cavities, by linking the typologies to their functions and potential re-uses and promotes archaeological and historical research for each case study. On the other side, it introduces technological innovation, by promoting 3D computer modelling of UBH, as a primary thrust for underground heritage research and development (e.g. 'seeing through the ground'), as well as detailed high-resolution reconstructions with the integration of different sensing techniques. The paper focuses on how cultural, scientific and technical knowledge of the underground built heritage, and specifically technological innovation, may assist local communities' decision-making, guaranteeing continuity of use and significance to the underground historic fabric, revitalisation of the public realm and skills development for townspeople. In particular, this approach pioneers socially and environmentally innovative solutions, by stimulating, developing and supporting processes of local community co-evolution and co-creation, which allows communities to explore alternative social trajectories in an adaptive, forward-looking manner, such as the Strategic Transition Management (STM). These tools can stimulate and facilitate local communities' empowerment and connect natural, social, cultural, political and economic environments, gauging impacts across different spheres of life, and grasping the importance not only of 'hard' but also of 'soft' infrastructures.