Kenya
On most days, the closest you'd get to sharing the trail with a Kenyan is probably several miles behind. Not so on this new running safari, a 12-day pounding that places you on twice-a-day runs with some of Kenya's most gifted athletes. You'll start in Eldoret, a city about 200 miles northwest of Nairobi and the heart of the country's long-distance scene. Next you'll team up with 1997 and 1998 Los Angeles Marathon winner Lornah Kiplagat in her hometown of Iten for runs through the verdant hills. The group—not the champ—sets the distance and pace. Most nights you'll sleep in basic accommodations in villages and get your carb-to-protein ratio right with meat pastries called samosas. Move on to Mombasa, where, on March 24, the World Cross Country Championships unfold—the first time Kenya will host the prestigious race. March 14–25; $3,900; Micato Safaris, 800-642-2861, micato.com

INDIA
The Tons River
The Tons River roars from 20,000 feet in the Indian Himalayas with such sustained intensity—think 55 miles of nearly continuous rapids—that the river hasn't seen a single paddler since whitewater pioneer Jack Morison first rafted it in the 1980s. Now the whitewater gurus at New Delhi-based Aquaterra Adventures have reopened the river to expedition-style, 11-day rafting trips, using upgraded equipment like self-bailing boats that were unavailable in Morison's day. Start at Camp Lunagad, about 270 miles north of New Delhi, and spend the next seven days floating through chilly glacial runoff that boils into Class IV–V rapids. Come evening, pitch tents in alpine meadows redolent of rhododendron and chir, and mingle with Gujar tribesmen. April 24–May 4; $1,250; info@treknraft.com

COLORADO
The Colorado Trail
Of all the big hikes that run across U.S. wilderness, few pack as much awe per step as the Colorado Trail. But tackling all 482 miles from Denver to Durango, through six wilderness areas and eight mountain ranges, would take you about a month. Instead, concentrate your efforts during a ten-day romp along a remote 95-mile ribbon that runs just east of San Luis Peak to Molas Pass, in the southwestern part of the state. Start at Spring Creek Pass, 33 miles northwest of Creede amid the 13,000-foot-plus San Juan Mountains. Plan on grinding up to 15 miles a day along airy ridges, down steep gorges, and up winding switchbacks. You'll spend four days cruising above tree line, at nearly 12,000 feet, and the closest you'll come to a town (Lake City) is about 17 miles, which means tackling thousands of vertical feet each day with a heavy pack. Take a break and frolic in Snow Mesa, a flat, grassy expanse so huge it takes a few hours to cross. 303-384-3729, coloradotrail.org

COSTA RICA
There may come a time—perhaps after your third endo over the handlebars—when pedaling 160 miles across Costa Rica by mountain bike makes an overcrowded bus tour look appealing. But keep riding—you won't regret it. Head out from San José for about 20 miles a day and 14,000 feet of total climbing to eventually reach the town of Nosara, overlooking the Pacific. For eight days you'll pedal Specialized hardtails (or your own bike) into villages where people still get around by oxcart, spending nights in hotels, research stations, and a private home tucked into a misty cloudforest. Get off the bike to bushwhack through monster ferns to reach the summit of Cerro Chato, a 3,937-foot sleeping volcano. When you slip into a hot spring near the 5,741-foot Arenal Volcano, your sore muscles will melt away. $2,596 per person with your own group of four; Serendipity Adventures, 877-507-1358, serendipityadventures.com

GREENLAND
Arctic Circle
When Fridtjof Nansen became the first to schlep across the Greenland ice cap, in September 1888, he studied Inuit culture, weathered minus-50-degree storms, and spent a cold, dark winter waiting for a ship to take him home. Today, adventurers can follow his tracks along the Arctic Circle using kites to pull them on skis—at about 12 miles per hour—under the guidance of polar explorer Matty McNair. Never skied behind a kite? You'll spend a few days on Frobisher Bay, on the southeast coast of Canada's Baffin Island, learning techniques that advanced skiers can pick up quickly. Then hop a two-hour flight to Greenland for a 345-mile trek, where the kites will help you pull a 150-pound pulk (loaded with tents, stoves, and beef jerky) in 20-below temps. The adrenaline rush will diminish the hardships as you rip in 24-hour sunlight through a landscape of dizzying white. May 1–31; from $5,000; NorthWinds Polar Expeditions and Training, 867-979-0551, northwinds-arctic.com