Yellowstone National Park, WY
Considering that Yellowstone was the country’s first national park, its popularity is expected. But come winter, humans largely surrender the park’s expansive landscape to its natural inhabitants—which makes for an ideal time for the intrepid traveler to appreciate the park’s crowd-free fragility, whether on horseback, snowshoes, cross-country skis, or your own two feet.

Great Smoky Mountains National Park, TN & NC
Although Great Smoky Mountains National Park sees more visitors year-round than any other park, winter is its lightest tourist time. Besides being especially accessible to East Coasters, the North Carolina-Tennessee scenery is pretty overwhelming—even when under a sheath of downy white. Half the winter days have highs in the 50s, and snowfalls usually occur only in the highlands.

Hiking and Camping in Death Valley National Park, CA
If winter's getting you down, 134 degrees might sound kinda nice. Fortunately this broiling Death Valley National Park record high doesn't happen in the winter months; the ominous-sounding park remains comfortably mild for outdoorsy types craving a break from the chill. Death Valley's low-elevation hikes are usually off-limits to summer hikers because of the heat, but in the winter, all 3.4 million acres are fair game. Hike from the country's lowest point—282 feet below sea level—right on up to Telescope Peak for panoramic views (from 11,049 feet) of the High Sierra and Death Valley.

Snowshoe, Cross-Country Ski, and Winter Camping in White Mountain National Forest, NH
Both the Forest Service and the Appalachian Mountain Club give a lot of TLC to the White Mountain National Forest, making it an ideal year-round destination. But the snow-kissed winters will give you an entirely new perspective on this New England gem. Nordic types can cruise through hardwood forest and past great White Mountain vistas on maintained cross-country trails. Or try your hand at backcountry trails in the forest's Pemigewasset Wilderness, where moose sightings are frequent. Winter camping is even available for the truly adventurous in scenic spots such as the Great Gulf Wilderness in the Presidential Mountains.

Hike in William B. Bankhead National Forest, AL
Mountains in Alabama? That's right. Bankhead National Forest contains part of the Warrior Mountains, the western terminus of the Appalachians, and there's more deep-wood beauty here than you could ever imagine. The forest is alive year-round, so you can hike through deep hollows, past sprawling lakes, and over upland ridges in the middle of winter. Be sure to visit Bankhead's star, the Sipsey Wilderness. This 24,922-acre playground is often called "The Land of a Thousand Waterfalls," for reasons you can probably imagine but should definitely see for yourself.

Multisport in Na Pali Coast State Park, HI
You'd be hard pressed to witness a temperature drop below 60 degrees on Hawaii's Na Pali Coast. Pali is the Hawaiian word for cliffs; a fitting name in this rugged landscape of deep, narrow valleys that shoot out to the ocean. The 11-mile Kalakau Trail, the only on-foot access to this part of Kauai's coast, traverses five lush valleys and crosses above high sea cliffs for incredible views. An abundance of tropical plants paint Na Pali's green valleys, but keep your eyes open for extremely rare native species that dwell in the hard-to-reach cliffs. After hiking the Kalakau Trail, explore the Na Pali Coast's shores by sailboat or underwater with a snorkel, even in January.

Snowshoe and Cross-Country Ski in Mount Rainier National Park, WA
Camp Muir, at 10,080 feet on Mount Rainier, buzzes all summer long with the excited hum of climbers waiting to make their summit attempt. But when winter comes to the mountain, the crowds dwindle, and the Paradise area on Rainier's southwest side, is the place to be. During the holiday season, rangers lead free guided snowshoe walks. Or you can rent cross-country skis and snowshoes at nearby Longmire. Though the area offers terrain free from avalanche danger, it's still best to come prepared for severe winter weather. The park service plows the road to Paradise during the winter months, making this unique experience possible. But you'll still want to carry tire chains, just in case.

Camp in Lake Havasu State Park, AZ
When a winter chill takes over the northern states, escape to Lake Havasu State Park, where the 60- to 70-degree temperatures will make you question whether you ever want to leave. As the park's name implies, the main attraction here is Lake Havasu and its scenic shoreline that welcomes winter campers. Arizona parks are popular this time of year, but you're sure to find a nice spot along the 45-mile lakefront, sometimes called the Colorado Coast. The beaches, boats, and campground grills beg you to sit back and relax, but there's also ample opportunity to get active. Hiking trails abound, as do bass-fishing tournaments in January.

Wildlife Viewing at Harriman State Park, ID
Harriman State Park lies within an 11,000-acre wildlife refuge in the greater Yellowstone Ecosystem, an 18-million acre area that is one of the largest, relatively intact temperate zone ecosystems left on Earth. Harriman is prime real estate for spotting wintering bald eagles and trumpeter swans. Get the best views by cross-country skiing or snowshoeing to the Jones House warming hut near Henrys Fork. You'll likely see moose, elk, and Sandhill Cranes along the way, too. Enjoy the park for the day, or stay overnight in a yurt, ranch house, or a dormitory-style room. Also, don't confuse this Idaho state park with Harriman State Park in New York, although that's another good one to explore.

Albert E. Sleeper State Park, MI
It's temping to stay inside by the fire when it's cold out, but Sleeper State Park gives you so many reasons to get outside. The park is on Michigan's "thumb," and offers opportunities for camping, skiing, snowmobiling, ice fishing, photography, quiet walks, and even bird watching. You can also enjoy Candlelight Trail evenings, in which hiking, snowshoeing, and cross-country skiing trails are illuminated for a truly unique recreational experience. It's almost like having the warming glow of your living-room fire out on the trail with you.