Thirty feet below us is a five-hundred-yard tunnel dug through solid granite, pitch black and glazed with ice, one in a series of tunnels that took Chinese laborers almost two years to excavate. These are the Donner Summit tunnels, blasted by hand some century and a half ago; below us is Tunnel 6, the Great Summit Tunnel. We cross a gently sloping snowfield, cut downslope, and suddenly greet a cavernous maw punched into the mountainside. The tracks that once ran through these tunnels are long gone. While we walk through the tunnel, our snowshoes crunching on the glossy ice, our headlights barely pushing through the darkness, I feel a profound sense of awe.