Subterranean construction is a recurring yet variably understood aspect of human activity across regions and periods. Underground systems in Turkey, Malta, Austria, and Bosnia and Herzegovina provide an opportunity to compare how such spaces were created, modified, and ultimately closed. The present study focuses on four representative contexts: the Derinkuyu Underground City, the Hypogeum of Ħal Saflieni, the Erdstall tunnel systems of Austria, and the Ravne tunnel system in the Visoko region of Bosnia and Herzegovina. Rather than assuming predefined functions, the analysis is based on observable structural and material characteristics, including construction methods, geological context, spatial organization, access control, and evidence of modification and closure. Particular attention is given to identifying patterns of intentional sealing, blockage, and infilling within these systems. The results indicate that subterranean construction is expressed through diverse architectural forms, ranging from carved multi-level complexes to narrow passage networks and modified underground corridors. While many systems demonstrate controlled access through architectural features such as constrictions or blocking elements, large-scale and systematic backfilling is comparatively rare. The Ravne tunnel system presents a distinct case characterized by extensive anthropogenic infill, complete floor-to-ceiling closure of passages, and the repeated use of dry-stone walls to segment and seal sections of the network. Stratigraphic evidence further suggests multi-phase modification and closure processes. The comparison supports the interpretation that the closure of subterranean space represents a deliberate, structured form of human activity rather than a passive consequence of abandonment. By focusing on construction and termination processes, this study contributes to a broader understanding of how underground environments are created, managed, and transformed.