The chapter studies Edward Bulwer-Lytton’s The Coming Race (1871) and Gabriel Tarde’s Underground Man (1896). Drawing on the pictorial and literary reception of the Thames Tunnel and the Parisian underground, the chapter investigates how the material change of subterranean space in nineteenth-century Britain and France stimulated the conception of a “new” underground associated with the technological future. Comparing the two authors’ intersection of the new underground with climate control, it ventures that Bulwer-Lytton Lytton demonstrates the calamitous aesthetic consequences of climate technology employed by an underground race. In contrast, Tarde portrays the flourishing of decadent underground civilisation prompted by the heat death of the sun. The chapter concludes that the discursive network turning the underground into an inorganic, climate-controlled place peaks in Underground Man, where the climate becomes an engineerable simulacrum, spelling out a progression from dystopian to utopian depictions of deliberate climate change.