The most remote raft trip in North America runs straight through the heart of northwestern Canada’s Ivvavik National Park, said Kevin Fedarko in National Geographic Adventure. The 2.4-million-acre Ivvavik, known as the “Serengeti of the North,” is larger than Yosemite and Grand Canyon national parks combined. With no roads or trails, “it is remote in a way that is ferocious and primordial.” A herd of 112,000 caribou live here, along with wolverines, grizzlies, polar bears, and musk oxen. “The only reasonable way to see” this Arctic wilderness is on a journey down the Firth River, which runs through the park’s core. Only seven commercial expeditions are allowed on it each season.

A dozen of us recently gathered in the mining settlement of Inuvik, boarded a bush plane, and flew 90 miles to a meadow on the banks of the Firth. The next morning, we began “our float north through the mountains to the sea.” The first three days were mostly uneventful. We drifted in three rafts down the river, catching trout for our suppers. On the fourth day, we reached the British Mountains, where the river narrowed and dropped into a 30-mile-long, 400-million-year-old limestone canyon, whose cliffs rose 20 stories above the water. On the eighth day we exited the mountains and arrived “at the doorstep of another world.”

The river entered a coastal plain braided with channels and capillaries interspersed with sandbars. Jutting out of the tundra, “75 feet into the air,” was the rock outcropping known as Engigstciak, where Paleolithic Siberian hunters once scouted for caribou. We made camp here, enjoying the 360-degree view as the setting sun cast a golden 11 p.m. glow. On our final leg into the delta, we spotted a lone galloping caribou. The water grew shallower, and occasionally we had to drag our rafts across the tidal flats. The North Pole lay “another 1,400 miles beyond,” and a frigid breeze blew from the “impossible cold seas beyond the horizon.” We had reached the “salt-encrusted rim of the continent”—but as we bedded down at midnight, “polishing off the last of our booze,” it seemed we had reached the end of the earth.