Yosemite National Park, CA
Each winter, millions of Californians head for higher ground, and we don't mean New Age gurus. The state's Sierra and Cascade mountain ranges become winter playgrounds. And no area personifies the romance of the High Sierra—at any time of year—more than Yosemite National Park. Yosemite's three main areas for snowshoeing and cross-country skiing are Badger Pass, Crane Flat, and the Mariposa Grove. Badger Pass is by far the star of the show: The vistas at the end of the 10.5-mile trail to Glacier Point are unsurpassed. Rare for a national park, Badger Pass even has a downhill ski area, which is a wonderful family ski spot. Go for gentle runs and great scenery, not for the downhill challenge of your life.

Boundary Waters Canoe Area Wilderness, MN
Often referred to as the "Norwegian Riviera," Minnesota's north shore of Lake Superior is home to a huge network of cross-country ski trails, which extends north and west into the Boundary Waters Canoe Area. The Gunflint Trail Association is made up of the lodges that dot this 60-mile stretch of winter heaven from Grand Marais, Minnesota, up County Road 12, and into the Sawtooth Mountains. These establishments team up to maintain the Nordic trails and cater to aerobic vacationers; most offer both ski rental and lessons. Also, don't miss the great dog-sledding opportunities in the park.

Galápagos Islands National Park, Ecuador
Biologists and naturalists recognized the Galápagos Islands' unparalleled uniqueness long before the park became Ecuador's first in 1959. The splendidly isolated archipelago, 600 miles off the coast of Ecuador, represents the earth's most important microcosm of untouched evolution. In addition to sanctioned, on-land nature-viewing, underwater exploration—whether scuba diving deep into the volcanic reef or snorkeling adrift on the current—opens up another world in this already dizzying realm. Calm seas and warm temps make December a great time to visit.

Everglades National Park, FL
Starting out from just outside Naples in southwest Florida, the 50-mile Tamiami Trail Scenic Highway will take you into the heart of one of America’s last topical wilderness: the Everglades. The wetlands of Big Cypress National Preserve (adjacent Everglades National Park) protect rare orchids, the endangered Florida panther, and a thriving ecosystem under siege from the demands of agriculture and urbanization. December starts the dry season in the park, meaning fewer insects, exceptional bird-watching, and more comfortable temperatures.

Allegheny National Forest, PA
Located in northwest Pennsylvania, the Allegheny National Forest spans an area of more than a half million acres offering superb outdoor recreation including hunting, fishing, boating, hiking, viewing wildlife, and camping. Despite the area's cold winters, cross-country skiers, snowmobilers, and ice fishermen brave the temperatures to enjoy the spruce and hardwood forests of the rolling landscape. Though most of the cross-country trails have a backcountry feel, Laurel Mill Cross Country Ski Trail is groomed all winter long.

Fiordland National Park, New Zealand
December means summertime in New Zealand, and with average daily highs of 68 degrees, it's the perfect time to hike the Milford Track, a spectacular 33–mile trail in Fiordland National Park. Stretching from Lake Te Anau to the Milford Sound, the trail covers one of the most breathtaking swaths of land in the world. Sure, this is the most popular season to hike the trail—for a good reason—but the government regulates the number of people who can access it. Be sure to plan well in advance to secure a spot on this trek; it’s well worth the effort.

Sonoran Desert National Monument, AZ
Located 63 miles southwest of Phoenix, Arizona, this monument gives "wide-open spaces" real meaning. Its 496,337 acres encompass three mountain ranges (with elevations ranging from 2,000 to 4,373 feet), several wilderness areas, wide valleys, and portions of the Juan Bautista de Anza National Historic Trail, Mormon Battalion Trail, and the Butterfield Overland Stage Route. Although the cool months are September to April, always bring plenty of water and don't forget to locate current trail maps. Be prepared for heat and flash floods, too. Then grab a hiking buddy and discover America's most biologically diverse desert.

Green Mountain National Forest, VT
Winter in the Green Mountain National Forest isn't for a slouch. Downhill and cross-country skiing and snowshoeing rule these parts when the white stuff falls. Snowshoeing can be enjoyed on well-marked trails or off-track for a more backcountry experience. Much of the fun of snowshoeing is in exploring brooks, beaver ponds, un-named hills, and general wooded areas. The entire forest is also open to cross-country skiing, though only trails shared with snowmobiles may be groomed. For downhill action, Sugarbush, Mount Snow, and Bromley are in the forest, and several other ski areas are nearby. It's a winter-sports paradise.

Tierra del Fuego National Park, Argentina
Tierra del Fuego is a place of extremes: the world's southernmost national park accessible from the world's southernmost city (Ushuaia). This is Argentina's only coastal national park, and water is a prime attraction. Think fishing, kayaking, maritime wildlife, stunning fjords, and transcendent seascapes. Tierra del Fuego also collectively refers to the scattering of islands, of which the park is part, separated from the rest of Patagonia by the Strait of Magellan. There’s plenty of adventure waiting on this isolated outpost for all outdoors enthusiasts.