Grand Teton National Park, WY
Grand Teton National Park's Mount Moran (12,605 feet) has been thunderously beautiful since its formation about five million years ago, but its fame is mainly due to Ansel Adams, who captured the imposing massif's image in his mural project. Today, most visitors choose to click away at the striking Oxbow Bend between Jackson Lake Junction and Moran Junction, where moose and other wildlife make frequent cameos. And though the days will be pleasantly warm in July, bring your rain gear for those ubiquitous summer-afternoon showers.

Pictured Rocks National Lakeshore, MI
America's first national lakeshore graces the north shore of Michigan's Upper Peninsula with long stretches of white beaches and 200-foot sheer sandstone cliffs that rise above. Lapping up the shoreline for some 42 miles is Lake Superior, a superlative mammoth of the Great Lakes—largest, deepest, coldest, and most pristine. Further inland you can watch bald eagles nesting atop old white-pine trees, hike deep into a mixed northern hardwood-coniferous forest, and fish interior lakes and streams teeming with steelhead and coho salmon. Though summer brings relatively warm temps to the park, the Lake Superior area is known for unpredictable weather. In other words, be prepared.

Glacier National Park, MT
Glacier National Park's legendary Going-to-the-Sun Road weaves through scenic stretches, past waterfalls, around glacial horns, and across the Continental Divide. Trailheads line the road, perfect for day hikes or multi-day treks. The ambitious can bike the 52-mile route; the vivid scenery may help you forget the 6-percent-grade climb and 3,400-foot vertical. Summer is the best season to visit the park, as almost all services and facilities are open.

Denali National Park, AK
Denali is on a truly Alaskan scale: six million acres—a plot of magnificent land larger than the state of Massachusetts—interrupted by just one road, and a gravel one at that, all but closed to private vehicles. In the summer, rivers rush wide and milky white with rock pulverized by glaciers, flower-studded tundra spills away in all directions, and wildlife such as caribou, Dall sheep, moose, and grizzly bears roam freely. And, if the weather cooperates, Mount McKinley dominates the horizon.

Masai Mara National Reserve, Kenya
Starting in July, a wave of more than 450 animal species flows through the northern Serengeti, as elephants, gazelles, rhinos, lions, cheetahs, leopards, wildebeest, and zebras flood across Kenya's Masai Mara National Reserve. Visitors linger on the fringes, snapping photos in startled amazement. Once the Mara's grass has been consumed in September, the roaming herds turn to tromp hundreds of miles to the southern Serengeti and Ngorongoro plains.

Crater Lake National Park, OR
Oregon's Crater Lake National Park has some of the most dependable weather of all the national parks—it snows here about nine months of the year. Summer temperatures rarely exceed the 60s, so if you're not one for sweating it out on a hike or grilling yourself at the beach, head to the High Cascades and plunge headlong into deepest lake in the U.S.

Killarney National Park, Ireland
At the heart of County Kerry, near the town of Killarney, three interconnected lakes shimmer through 25,000 acres of verdant woodland, the largest natural tract left in Ireland. July brings 60-degree weather to the park, perfect for outdoor adventures. The park provides the ideal cycling-walking-boating combination. Most open boats allow bikes on board, and after crossing the Upper Lake, you can return to Killarney by cycling the Gap of Dunloe or walking the Old Kenmore Road. Camping is not permitted in the park itself, but the lively neighboring town of Killarney offers a selection of B&Bs, as well as the requisite pubs for a post-hike pint.

Biscayne National Park, FL
Just south of Miami, this park boasts the longest stretch of mangrove forest remaining on Florida's east coast. And summer is when the shallow waters of the bay are the clearest, opening the window to a world of starfish, sponges, crabs, sea urchins, fish, and hundreds of other marine plants and animals. Though scuba diving and snorkeling are the star activities of this park, you can hike on Elliott and Adams keys, sea kayak in Biscayne Bay, and, not surprisingly, enjoy abundant saltwater fishing and lobstering.

Cape Cod National Seashore, MA
This 40-mile seashore boasts some of the world's most beautiful white sand beaches. It's a land of parabolic sand dunes, 19th-century lighthouses, shipwrecks, pilgrims, and piping plovers. Take off your shoes and wade barefoot in the calm waters of Pleasant Bay as fiddler crabs scurry over your toes. Explore White Cedar Swamp on an elevated boardwalk; it's an excellent example of the many Cape Cod swamps that thrive near "freshwater kettles" created by blocks of ice left by receding glaciers during the last Ice Age. Before you retreat back to the beach, kayak Salt Pond, a 40-foot-deep glacial kettle hole breached by the sea, and Nauset Marsh, an excellent viewing area for waterfowl and shorebirds.

Great Barrier Reef Marine Park, Queensland, Australia
Although it's World Heritage-listed, the Great Barrier Reef is home to activities that include commercial fishing boat, scientific research, and, of course, tourism. The reef, a 135,000-square-mile behemoth visible from outer space, is not merely a large-scale spectacular; its beauty extends to the billions of microscopic lifeforms supported by this blooming underwater ecosystem. July marks the middle of Queensland's dry season, which is the best time to be on the reef. But it's also the peak of tourist season. Hit up the Whitsunday Islands on the reef's southern end and avoid human contact for a while. Or further north, beyond Cairns' backpacker-focused vibe, the regions nearing Port Douglas are more serene and less touristy.