Welcome to Frostbite Falls

As ultras go, the Arrowhead 135 Ultramathon is an odd event, more akin to an Alaskan sled-dog epic than a century bike ride or triathlon. Widely considered Minnesota's most extreme endurance race, the race kicked off its fourth annual trek Monday, and requires competitors to combine athletic strength with survivalism, sending cyclists, trekkers and skiers solo and unsupported along the race's namesake 135-mile remote and rolling course.

You are given 60 hours to complete the course via one chosen mode of transportation - foot, ski or bicycle in the snow. You get a map at the start and follow a trail that fades in and out -- with forks and intersections mostly unmarked -- and a spinning compass needle as your sole guide.

The Ironman this is not. No one is in the woods to cheer. There are no water stops or hand-out energy gels. On the Arrowhead Trail, you haul all your own food and gear. You melt snow with fire to make water. You sleep, if need be, on the ground, a black sky above, stars pricking through, wolf prints in the woods out beyond your packed platform in the snow.

Most racers never finish, 60 percent surrender somewhere along the route. Last year, when the temperature dropped to minus-35 degrees during the night, only 10 of the 46 starters crossed the finish line at a lodge on Lake Vermilion, 135 miles and many cold hours down the line.

The natural beauty of the North Woods is a top draw for Arrowhead racers. Competitors come from as far away as Brazil and as nearby as Ely. Birch, pine and poplar trees make up most of the scenery, but frozen rivers, ravines, lakes, bogs, huge ridgelines, cliffs and slopes so steep many racers have to push their bikes up them create a course of ever-changing Ice Age-era topography.

Though maybe not suitable for your average, everyday runner, the Arrowhead 135 Ultra is a tough-as-nails race that will take you to the edge of your endurance limits and beyond.

But it's the kind of ride you'll likely never forget.