Deep beneath Greenland's ice sheet lies Camp Century-a clandestine U.S. military outpost engineered during the Cold War's zenith, powered by a portable nuclear reactor and conceived as the nerve center for Project Iceworm: a vast network of tunnels intended to conceal hundreds of nuclear missiles. Abandoned in 1967 after ice instability doomed the scheme, the site entombed thousands of liters of diesel fuel, PCBs, radioactive coolant, and other hazardous waste in a frozen vault now threatened by accelerating melt. Advanced radar imaging by NASA, coupled with the rediscovery of long-forgotten ice cores and basal sediments, has unveiled startling revelations. Plant fossils, pollen, and ancient microbial DNA testify to a Greenland that once sustained boreal forests and tundra ecosystems-ice-free as recently as 400,000 years ago-with global sea levels meters higher. These records expose the ice sheet's fragility and challenge long-held assumptions of its permanence, while models forecast the impending release of buried contaminants into pristine Arctic waters. This authoritative narrative illuminates the site's profound dual legacy: a monument to audacious military strategy and a stark harbinger of environmental reckoning. It scrutinizes the geopolitical tensions surrounding responsibility for cleanup, the strategic reawakening of Arctic resources amid receding ice, and the imperative of cutting-edge monitoring to anticipate ice-sheet collapse. Essential for historians, climate scientists, policymakers, and global citizens, City Under the Ice presents a gripping, evidence-driven account that demands immediate attention. The frozen remnants of Camp Century are no longer silent-they are awakening, carrying warnings that resonate far beyond the polar wilderness. The time to confront this legacy is now, before the ice surrenders its secrets to irreversible consequence.