Channeling the elusive and unruly materiality of air as a social, yet precarious medium, scholarship is mostly concerned with spaces aboveground. However, practices of sensing, measuring, and metabolizing (contaminated) airs as well as techniques of their regulation, control, and standardization also occur elsewhere: the subsurface. In their attempts to transform hostile spaces into contained and profitable environments, underground sites continue to engender both tropes of terrestrial-infrastructural progress and extractivist technocapitalist logics. Mining infrastructures have a long history of handling the potentially life-threatening impacts of underground air, for example, through sentinel species that detect toxic carbon monoxide. As such, the vulnerability of breathing bodies becomes a matter of transcorporeal, at times nonconsensual, bonds across species, particles, and infrastructural means. The chapter unfolds along two intertwined arcs: (1) a speculative material inquiry into the subsurface as a domain of compromised airs, sentinel breathing, and edge ecologies. This arc argues that the subsurface renders material processes in intricate ways. It engages leaking gases and fire penetrating the underground through the sociomaterial configurations of an abandoned mine. Permeable, oddly lingering, they invite a queer reading of their materialities. (2) An experimental process in collaborative speculation, conceptualized through a three-year transdisciplinary project framework, unearths the intricacies of breathing as respiratory communities. It attends to the urgencies and possible material futures of relating to compromised airs and asks what modes of critique such collaborative storytellings and trans-corporeal practices might hold, tying them back to the respiratory complex of sentinel breathing, cometabolizing, and extractive afterlives.