YosemiteFor scenery that will take your breath away, Yosemite National Park (nps.gov/yose) in central California is unmatched. Iconic granite cliffs such as the picturesque Half Dome and El Capitan, expansive vistas of glacier-carved valleys such as Tuolumne Meadows and Yosemite Valley, and the thunderous waters of Yosemite Falls and Bridalveil Fall act like balm to city-weary souls.
One of the best ways to see these jaw-dropping scenes is aboard a raft, floating along the gentle Merced River. But the rafting season depends on the water level, which drops off in late summer. So hit the river in late spring through midsummer. Bring your own raft, or rent small inflatable boats at the Curry Village Recreation Center.
Landlubbers can rent bikes to explore the paved paths that follow the river's route, or hike one of the dozens of trails that crisscross the park. Avid rock climbers know that Yosemite also offers world-class climbing opportunities. And camping enthusiasts will find a handful of campgrounds, which, though often crowded, offer better proximity to Yosemite attractions than the somewhat pricey in-park lodges.
YellowstoneThis geological hot spot that stretches across the western portion of northern Wyoming and southern Montana is the best place in the world to check out the spewing geysers, bubbling mud pots and gently stewing hot springs. In addition to the park's superstar, Old Faithful, geyser gazers will find hundreds of thermal features in the surrounding Upper Geyser Basin and nearby Midway Geyser Basin, site of the gloriously colorful, nearly 370-foot-wide Grand Prismatic Spring.
Yellowstone (nps.gov/yell) also is one of the best places in the lower 48 to spot wildlife. Bring binoculars or telescopes to look for massive buffalo herds moving slowly across the grasslands, lone grizzly bears galumphing along mountain ranges, stealthy wolves hunting beside waterways, and rival elk bucks crashing their massive antlers.
Grand CanyonA mile-deep gorge that stretches nearly 300 miles across northern Arizona, the Grand Canyon (nps.gov/grca) is ablaze with the fiery colors of eons of rock layers that tell the history of the geological world. Brightly hued rock outcroppings, ethereal stone spires, massive plateaus and innumerable hidden interior canyons offer hikers a lifetime of exploring via the several trails that lead into the heart of the abyss.
But for real adventure, book a multiday white-water rafting tour that takes hearty guests through virgin stretches of the Colorado River as it courses along the canyon floor.
RedwoodStand in awe alongside the tallest living organisms in the world at Redwood National Park (nps.gov/redw), in coastal northern California. This lush park, which also encompasses three state parks, preserves the remnants of a 2-million-acre forest of giants.
Don't miss the chance to hike the Coastal Trail, in the Prairie Creek State Park section, a day hike through redwoods that offers spectacular views of the ocean.
DenaliThe crown jewel of Denali (nps.gov/dena) in central Alaska is the perpetually snowcapped Mount McKinley (named Denali by Athabaskan tribes). The tallest mountain in North America stretches more than 20,000 feet skyward. Visitors will find this park wilder and less congested (and less accessible) than most other national parks.
The beautiful yet rough terrain and inhospitable climate (prohibitive for humans in all seasons except summer) and limited roadways (most of which are accessible only via park-operated tour buses) encourage wildlife to claim the park as their own. Mother grizzlies frolic with cubs as snow-white Dall sheep with whimsical whorling antlers scramble along rocky cliffs -- all seemingly oblivious to the presence of people.
For a peek at tamer animals, visit the park kennels, which house the sled dogs that make winter transportation possible for park rangers. During the summer, animal handlers conduct three demonstrations a day with these Alaskan huskies.