How can we cultivate an underground multispecies justice with beings whose lifeworlds are unknown and unknowable? This article examines this question through a consideration of stygofauna: miniscule deep-time creatures who make their home in the watery seams of the earth. Taking a cue from these critters—many of whom have evolved without eyes to make their way differently in the darkness of their watery subterranean homes—the article troubles the assumption that knowledge, care, and justice must be predicated on a kind of knowing that insists that humans literally bring other worlds to light. Through a specifically situated exploration of stygofaunal worlds, knowledge, and mining in Australia, the article asks, How is knowledge-as-illumination complicit with complex regimes of knowledge where knowing in the name of justice is tangled up in knowing as a further (colonial, speciesist, ableist) violence? Refusing purity politics, the article's first aim is to demonstrate our complicity with extractive knowledge regimes even in a quest to care for underground worlds. Second, the article insists that knowing otherwise is both possible and already at work. It argues that to know stygofauna otherwise, one cannot eschew science or knowledge altogether. Instead, it proposes that multispecies justice depends on two moves: first, on safeguarding a mode of unknowability that the article refers to as estrangement, and second, on recognizing and cultivating knowledge practices that can cultivate nonextractive relations with subterranean species, even if imperfectly. It concludes with a short overview of several examples of knowing otherwise that push readers to think differently about knowledge as a practice of care and justice.