What the ground says…

Ground, as a body incised by natural and human actions (European Landscape Conven-tion), carries “stories”, going beyond quantitative values. As in a text, it holds the keys to under-stand what it covers or hides. In its thickness, it shelters “implicit projects”. Understanding its complexity requires a physical and perceptual commitment, challenging the body in space: dimensions gradually forgotten by Environmental Sciences. As a “threshold” between visible and invisible, Underground‐Built‐Heritage represents the reverse of the emerged world: hollow space, both generator and mirror of open space (cities, landscapes). The focus is on physical and mental relationships between these two worlds. Past and present relationships emerge, allowing hypothe-ses to reconstitute collective memories, practices, knowledge, and values, which serve territorial development. The “Three Countries Park” is a place for cross‐border experimentation to test how UBH can rebuild common links for fragmented environments. The cavities of a geo‐park (planned) and the tangles of underground mining architecture are the fragments of a vocabulary whose meaning communities have to relearn. Built undergrounds will, thus, emerge from common stories that revive the imagination of populations who have lost all notion of belonging to a place. UBH will become a vector of new territorial coherence linking the physical and mental perceptions of people.