Steve Duncan spends his career mapping what lies beneath New York City, treating bridges, sewer tunnels, and subway tunnels as a second, hidden version of the metropolis stacked underneath the visible one. This film follows him and Norwegian adventurer Erling Kagge, who has climbed Everest and trekked to both poles, on an extended underground expedition through the city's subsurface infrastructure, sleeping where they travel rather than surfacing each night. Kagge treats the trip as continuous with his polar and mountain work, framing subterranean New York as unexplored territory in the same sense the poles once were. The camera follows the two men through drainage tunnels and structural undersides most residents never see, piecing together how the layers connect to the city's history and engineering above ground. The expedition drew outside attention too, covered on the front page of the New York Times metro section and reported on NPR, evidence that Duncan and Kagge had found something genuinely unmapped just beneath everyday streets.