The following are open year-round; call ahead for weather and road conditions.
1. Rocky Mountain Arsenal National Wildlife Refuge
A clean blanket of snow makes it easy to forget that this 5,000-acre refuge was once a chemical-weapons factory site. Now it's a sanctuary for wildlife, an island in Denver's encroaching development. Look for coyotes, great horned owls, mule deer, prairie dogs, and white-tailed deer. More than 100 bald eagles visit during the winter. Hike the easy 4-mile round-trip Woodland Trail into wetland, woodland, and prairie, or sign up for one of the free two-hour narrated tram tours that loop the refuge.
VIEWING TIPS: Late afternoon is the best time to look for bald eagles; you'll often see them roosting in cottonwoods. Ask about wildlife-photography workshops.
INFO: Tram tours are at 9 Sat and at 1 Sun (free; reservations required). The refuge is open 8–4:30 Sat–Sun (free). 10 miles northeast of downtown Denver at 56th Ave.and Havana St.; http://rockymountainarsenal.fws.gov or 303/289-0930.
2. National Bison Range
While the deer and pronghorn antelope don't exactly play here, they do roam with nearly 400 bison. The animals have a lot of room to spread out within the 18,700-acre refuge, so be patient when you drive the roughly 10-mile Prairie Drive/West Loop vehicle tour route. Stay in your car (it acts as a blind) and scan treelines and down into the brush. Don't bypass the visitor center, even though it's closed on weekends ― the short nature trail is bird-rich, with great horned owls, pygmy owls, and saw-whet owls.
VIEWING TIPS: Early in the morning, you may see owls still hunting. Visit on a clear day to see more animal action.
INFO: Missoula, MT, is the best base for lodging and dining  or 406/543-6623. The range is off State 212 about an hour's drive north of Missoula;  or 406/644-2211.
WEST YELLOWSTONE, MT
3. Grizzly & Wolf Discovery Center
This nonprofit center on the western edge of Yellowstone National Park offers a naturalistic setting that lets you get close to both grizzlies and wolves ― rare in the wild. You'll see any of eight bears wrestling or foraging for food hidden in the 2-acre habitat. You can also observe the six wolves of the nearby Gallatin Pack habitat. The alpha (dominant) male holds its tail straight up in the air.
VIEWING TIP: The wolf pack howls a lot in winter, mostly in the morning and evening. INFO: For West Yellowstone lodging and dining, contact the West Yellowstone Chamber of Commerce  or 406/646-7701). The discovery center is open 8–5 daily (until 5:30 Jan 21–Feb 10); $9.75, $5 ages 5–12, $9 ages 62 and over. 201 S. Canyon St.; , 800/257-2570, or 406/646-7001.
4. National Bighorn Sheep Interpretive Center
Just outside Dubois, the Whiskey Mountain Habitat Area gets up to 700 sheep from mid-November through March ― the largest group of wintering bighorn sheep in the Rockies. Even though the rut is over, you may still see sparring and head-butting among the rams now.
VIEWING TIP: Midday is best for spotting sheep ― they're lower down on the mountain, feeding and sunning.
INFO: The best base for lodging and dining is Jackson (www.jacksonholechamber.com or 307/733-3316). Reserve a guided wildlife tour, offered daily through Mar ($25, includes van tour and use of binoculars and spotting scopes). Interpretive center open 9–5 daily; $2, 50 cents ages 12 and under, $5 per family. 90 miles east of Jackson via U.S. 26/287, at 907 W. Ramshorn St.; , 888/209-2795, or 307/455-3429.
MAMMOTH HOT SPRINGS, WY
5. Yellowstone National Park
Animals rule this park in winter, but cars are scarce ― though you'll see some snow vehicles ― because only one park road is open to autos. At the park's north end, you can drive to wildlife-rich Lamar Valley on U.S. 212 (open ― but not plowed daily ― from Gardiner to Cooke City, Montana). Even better: Join guided cross-country ski, snowcoach, or snowmobile tours for more wildlife-viewing here or in the Upper Geyser Basin; most trips leave from Mammoth Hot Springs or from West Yellowstone, Montana.
VIEWING TIPS: At Mammoth Hot Springs, you may see elk any time. In Upper Geyser Basin, look for bison or elk grazing on exposed grasses around hot springs.
INFO: Stay in the park at Mammoth Hot Springs Hotel (97 rooms from $73) or at Old Faithful Snow Lodge (134 cabins and rooms from $80; accessible only by snowcoach or guided snowmobile). For lodging and details on snowcoach tours, visit  or call 307/344-7311. Join winter wildlife activities led by park rangers or the Yellowstone Association Institute  or 307/344-2294. $20 per vehicle for seven-day park pass. www.nps.gov/yell or 307/344-7381.