Underground Built Heritage (UBH) is a distinct class of cultural heritage providing a focal point for community pride and engagement to become a springboard for local sustainable development (LSD). This research aims to articulate how local UBH and its fringe serve as a facilitator of communal identity to mobilize community care towards social and economic development with less involvement from the state and the market actors. For this purpose, local (and less-conspicuous) cases of UBH are employed in Warsaw, Poland, and Volos, Greece, indicating the power of UBH to connect and engage local communities with places, triggering a momentum for a truly bottom-up action that pays less attention to market considerations and state support. The studied UBH sites have been discussed according to an established common framework, dealing with five main issues: (a) general context and status, (b) history, (c) users and management, (d) ecosystem services, and (e) introduction of the paradigm of living labs. The analysis was based on a thorough literature review and complemented by field observations and interviews. The results provide evidence for UBH as a potential facilitator of social and economic development. The case studies in Poland and Greece showed that local actors were involved in activities and social networks of tacit knowledge, generating community building to reinforce bottom-up activities in contact with UBH.