For billions of years, Venus may have been a world not unlike our own — temperate, watered, and perhaps even welcoming to life. Then, from within, the planet undid itself: vast rivers of carbonatite lava carved channels across its surface, exhaling carbon dioxide in quantities sufficient to unravel an entire climate. What Venus became — a crushing, 460-degree inferno — is not merely a curiosity of our solar neighborhood, but a reminder that habitability is a condition, not a guarantee, and that the forces capable of ending it may already be present beneath a world's surface.