Shortly before packs of huskies and their hardened sled drivers descended on Alaska’s Iditarod Trail in March 2000, a different creature claimed the 1,000 miles of frigid frontier: an almost 80-pound, plumped-up piece of steel, gears, and spokes. At the first Iditasport Impossible, Grand Junction’s Mike Curiak rode a bike with 3.5-inch-wide tires, almost double the width of the tires on standard mountain bikes. The fatter tires allowed Curiak to stay on top of the soft snow without sinking, and he bested the trail in 15 days, blasting the route’s previous record for human-powered travel (as in: sans dog) by six days. Fifteen years later, fat bikes—with tires now up to five inches wide—are being used as much for recreation as for testing the limits of human fortitude. U.S. sales increased 248 percent between 2013 and 2014, according to NPD Group, a market-research company. Colorado is no exception, with a bevy of mountain spots beginning to cater to fatties, from dedicated trails at Snow Mountain Ranch between Winter Park and Granby to Hotel Telluride’s Snow Bike & Brew package, which debuted in late November. And trying the trend just got easier with this handy guide to fat-biking fun.

The In-Town Adventure

Dirty Bismark, Boulder County

Difficulty: Easy or moderate

After snowstorms, this trail system becomes a winter wonderland for fatties. A mirror of the Morgul-Bismark road loop, Dirty Bismark is a choose-your-own-adventure spot: Beginners enjoy the three-mile Marshall Valley-Community Ditch-Coal Seam loop; although the entire 15.5-mile loop (with a gain of 1,522 feet in elevation) isn’t super technical, it’s pretty tough on mortals.

Rent: University Bicycles, $50 to $90 per day

The Ride Through Time

Mineral Belt Trail, Leadville

Difficulty: Moderate

This 11.6-mile route is more than a workout; it’s also a glimpse into our state’s rich mining history. The loop, which gains about 1,000 feet total, passes relics such as the Matchless Mine, Horace Tabor’s silver-rich fortune maker. And you’ll have a smooth view of the past—not to mention the Sawatch and Mosquito mountains—thanks to snow groomed for cross-country skiing.

Rent: Cycles of Life, $50 per day

The Guided Ride

Breck Bike Guides, Breckenridge

Difficulty: Easy or difficult

Breck Bike Guides takes newbies to the town’s scenic, well-used trail system. If you crave a more exciting exploit, Breck Bike will chaperone you on an advanced loop through the Hermit Placer, Moonstone, and Wellington trails outside town. Your fearless leader costs $35 an hour, plus $10 for each additional rider, but there’s no better way to find secret stashes of snow.

Rent: Breck Bike Guides, $40 for a half day (sans guide)