Great Sand Dunes National Park, CO
Despite being one of the nation’s newest national parks (inscribed in fall 2004), the sculpted dunes of Great Sand Dunes National Park go back about 12,000 years, when melting glaciers deposited huge quantities of silt, sand, and gravel on the floor of the San Luis Valley. Heavy winds carried much of this material back toward the Sangre de Cristo Mountains, which then acted as a dramatic rocky backstop for the sandy, shape-shifting landscape.

Golden Gate National Recreation Area, CA
Dominating San Francisco Bay like the prow of a super tanker, San Fran almost yearns to break from its urban shackles. Almost one-tenth of the city is given over to parks and playgrounds, while the amorphous 74,000-acre Golden Gate National Recreation Area has a footprint twice the size of the city itself. Suffice to say, locals like to play outside. Don't miss the exceptional Muir Woods National Monument within the recreation area's borders, which is known for its sanctuary-like old growth stand of coastal redwood trees.

Chugach State Park, AK
Half-million-acre Chugach State Park is the country’s third-largest state park, all the more remarkable because it virtually spills into downtown Anchorage. Not surprisingly, locals and visitors alike take full advantage of this natural jewel, whether it’s a short summer hike up 3,550-foot Flattop Mountain, casting a line for Dolly Varden, or executing some technical footwork over the park’s 500-plus glaciers.

Grand Canyon National Park, AZ
Test your nerves of steel on the Grand Canyon Skywalk, an all-glass, open-air skywalk that hangs 4,000 feet above the canyon floor and 70 feet beyond the rim. Prefer to stay on the ground? The Kaibab Plateau-North Rim Parkway, named after the region the Paiute Indians called “the mountain lying down,” is a 42-mile scenic byway extending south from Jacob Lake through Kaibab National Forest right up to the Grand Canyon’s spectacular (and less crowded) North Rim. Follow the path, yes, but no Thelma and Louise denouements, please.

Sleeping Bear Dunes National Lakeshore, MI
Venture to the northern Lake Michigan area in the warm-weather months for a week and you'll be treated to far more than a fun frolic in a great lake. Explore the region at a slow pace on bike or on two feet and discover its diverse terrain, from the rolling countryside of the Leelanau Peninsula to the steep sand piles of Sleeping Bear Dunes National Lakeshore.

Monongahela National Forest, WV
Tucked in the deep forests of the Allegheny Mountains, just beside the Elk River, the tiny town of Slatyfork serves as a hub for some of the East's best mountain biking. Locals boast that they've got 200 miles of trails just outside their doors, and innumerable more twist through the 919,000-acre forest. It's diverse territory, too. Technical singletrack lies just minutes away from a more gentle rails-to-trails route. A couple of resorts, the Elk River Touring Center and Snowshoe Mountain, offer guided tours and uphill shuttles.

Hells Canyon National Recreation Area, OR & ID
Although not as dramatic as the Grand Canyon, 8,000-foot-deep Hells Canyon lives up to its name in depth. As the deepest gorge in North America, the canyon's walls cast ominous shadows across the rafters that dare the Class III and IV rapids of the Snake River, its architect.

Sequoia and Kings Canyon National Parks, CA
Come May, it may seem odd to think of snow when most people are airing out their Speedos for Memorial Day pool openings, but California's Sierra Haute Route is one reason to keep the planks out just a few weeks longer. This 38-mile romp dissects the wild spine of 865,952-acre Sequoia and Kings Canyon national parks and will introduce both skiers and 'boarders to some of the most remote and rugged backcountry the West Coast has to offer.

Sagarmatha National Park, Nepal
This park's literal highpoints, Everest, Lhotse, and Cho Oyu, are three of the world's highest peaks and certainly get their fair share of attention. But the surrounding Himalayan-highland parkland should not be overshadowed. UNESCO granted Sagarmatha National Park World Heritage status in 1979 for its pristine wilderness, rare animals such as snow leopards and the Himalayan red panda, and unique Sherpa culture. Visit in May before the monsoon season drenches the Himalayas.

Copper Canyon, Mexico
The canyon's primary inhabitants, the Raramuri, are among the most intriguing aboriginal cultures in the northern half of the Americas. Known for their endurance, the Raramuri are said to possess unbelievable stamina and speed, and are able to outrun deer. Long before our ultra-marathons, they competed in races that stretched non-stop for more than 100 miles at a time. Hikers will need some of that Raramuri spirit to fully explore the Copper Canyon's labyrinth of 200 gorges, which form a series of six massive, interconnected canyons, each one larger than Arizona's own Big Ditch. And there's plenty of singletrack winding through these canyons—it's a mountain biker's dream.