The day begins before sunup in Jackson — a handful of headlamps bob toward the van, breath white in the cold. By 7 a.m. you’re fitted into a windproof suit, handed a helmet and goggles, and led to a line of snowmobiles that hum like patient predators. The machines take off into a landscape that was carved by fire and ice: steaming fumaroles and bleached rhyolite canyon walls slide by as the guide opens the throttle for long runs across packed park roads. Over roughly 65 miles and eight hours on snow, the route threads past Yellowstone Lake and drops you at the rim of the Grand Canyon of the Yellowstone to stare up at the 308-foot Lower Falls.