Climb at Rumney, NH
September's cooler temps bring a blanket of color across New England's forests. They also mean better friction and the perfect time to make a pilgrimage to Rumney, arguably New England's best sport climbing area, with some 400 mica-schist routes between 5.4 and 5.14. Take a minute to marvel The Fly, a 5.14d with amoeba-sized holds ascended by climber Dave Graham, then move on to the Main Wall, which features routes from 5.2 to 5.13d.

Bird Watch on the Colonial Coast Birding Trail, GA
A preponderance of salt marshes, old rice fields, woodlands, wetlands, and shoreline makes Georgia a veritable explosion of birds in spring and fall. Go in September and October to follow the Colonial Coast Birding Trail, whose 18 sites include the Cumberland Island National Seashore and Harris Neck National Wildlife Refuge. Terns, endangered wood storks, and brown pelicans are among the 300-some species you may spot in this Atlantic flyover area.

Road Bike Skyline Drive, Shenandoah National Park, VA
As kids head back to school and fall commences, traffic disperses from Shenandoah National Park's stunning 105-mile Skyline Drive. Trace the crest of the Blue Ridge Mountains by bike and you'll come across some 75 scenic overlooks of the Shenandoah Valley and wildflowers such as goldenrod and black-eyed susans lingering well into autumn. After riding a section of the drive, apple-smoked pork and blackberry-ice-cream pie await at the historic Big Meadows Lodge.

Backpack the John Muir Trail, CA
Granite cliffs, three-story trees, and 14,000-foot mountains might make hikers feel Lilliputian in this landscape of the Sierras. But that is exactly the point. Escape city life on the 211 challenging miles of the John Muir Trail to see three national parks, two wilderness areas, and countless Sierra vistas. In early September, the summer crowds and mosquitoes have dispersed, but the days are still warm.

Mountain Bike the North Umpqua Trail, OR
It can start dumping snow in southwestern Oregon's Crater Lake, which sees some 40 feet annually, as early as October. But September is a perfect little weather window between the sticky summer and wet winter. Choose a section of the 79-mile North Umpqua Trail, which runs through old-growth Douglas fir stands to the spine of the Cascade Range, east of Roseburg, Oregon. Umpqua Valley wineries, known for producing tasty Rhone varietals like syrahs and viogniers, make perfect post-ride stops.

Canoe the Niobrara River, NE
If you equate Nebraska with the monotony of cornfields along Interstate 80, think again. The northern border of the state harbors a trove of forested hills, prairie, waterfalls, and cliffs—all bisected by the Niobrara River. Meet up with a guide in Valentine, Nebraska, and paddle the 76-mile stretch designated a national scenic river. Herds of bison and elk aren't uncommon along the banks.

Sail the Dalmatian Coast, Croatia
The secrets of Eastern Europe's charms have officially leaked. Now Croatia, the region's crown jewel, is veritably packed with gapers, who come for the azure Adriatic, rocky shorelines, and lush national parks. Instead of terrestrial travel, skip from town to town in seclusion on a sailboat while snorkeling, beaching bumming, and exploring some of the 1,110-plus islands that dot this 1,100-mile coastline.

Trek in Yunnan Province, China
Tucked in the south-central nook of China, Yunnan is closer to Tibet, Laos, and Vietnam than Biejing. Its striking diversity of landscapes and ethnicities, like the Naxi, Yi, and Tibetan minorities, is starting to make it a hub of adventure travel. Peek into the ancient city of Lijiang, lined with stone streets and canals, before heading into the hills. Tiger Leaping Gorge, a plunging canyon carved by the Yangtze River and lined with terraces, is one of the area's best treks.

Kayak the Sian Ka'an Biosphere Reserve, Mexico
The high-rise hotels and packed beaches of Cancun may not be your scene, but go a hair south of the spring-break hot spot and you'll find the Sian Ka'an Biosphere Reserve, a more pristine version of the Mayan Riviera. Here, some 300 species of birds flourish in mangroves, marshes, and forests. Explore the reserve by kayak with the Centro Ecologico Sian Ka'an (+52.984.871.2499; www.siankaan.org), an education and ecotourism center run on renewable energy and operated by locals. Proceeds help fund conservation of the 1.3-million-acre reserve.

Watch Wildlife in the Okavango Delta, Botswana
Jeeps, feet, and dugout canoes are all perfectly viable means of exploring Botswana's Okavango Delta, one of earth's largest inland deltas and, come summer, a maze of channels, islands, and floodplains. All of this clear, cool water, which flows from Angola into the Kalahari sands, brings flocks of birds, from owls and cranes to eagles and geese. Visit both land-based and water-based lodges to experience the delta's different ecosystems.