Kayan Mentarang National Park, Indonesia
Kayan Mentarang, on the verdant island of Borneo, is one of the last remaining homes to the rhinoceros hornbill and strange primates like proboscis and leaf monkeys. The big draws for tourists (and poachers) are the adorably petite Sumatran rhino and the Borneo pygmy elephant.
How to Go: Asia Transpacific suggests a six-day itinerary beginning at the village of Long Layu. Local Dayak tribes still live in communal dwellings and guests do, too, as there is no accommodation in the park.
The Upper Paraná originally measured 182,000 square miles, but with only 7.4 percent of pristine area remaining, it’s now one of the most endangered rainforests on earth. More than 90 percent of amphibians and 50 percent of plants found there are unique to the area, and according to the World Wildlife Fund, it’s an outstanding ecoregion that represents a complete range of the planet’s freshwater and saltwater habitats. But it’s also home to more than 25 million people, making it one of the most accessible—and threatened—intact forests.
Blaine Harrington III/Corbis
The northern boreal forests occupy great swaths of land from Alaska’s dramatic Denali National Park all the way to the Wood Buffalo National Park in Alberta, Canada (at 17,000 square miles, it’s the largest national park in the country).
How to Go: Country Walkers’ six-day trek aims to give visitors an experience from every angle: from the ground (hiking), from the air, and from a train. Bed down at North Face Lodge with spectacular views of six major peaks of the Alaska Range.
Daintree National Park, Australia
At 160 million years old, this UNESCO World Heritage–listed spot in Oz’s far northeast region is one of the oldest undisturbed forest ecosystems on earth. It’s also a birder’s paradise—more than 430 avian species live in the forest, including 13 found nowhere else on Earth. And it’s home to the weird and wonderful peppermint stick insect: colored like candy, the creature creates a peppermint aroma to ward off predators. The Maardja Boardwalk (an easy stroll even for a lethargic walker) displays the transition from freshwater rainforest to saltwater mangroves.
Primorsky Kray, Russia
These cool-climate boreal forests, stretching from Finland in the west to the maritime province of Primorsky Kray (bordering the Japan Sea) in the east, hold the title as the largest ecosystem on earth. The bucolic Primorsky Kray is the most intact region accessible to tourists; more than 80 percent of the forest remains.
How to Go: Local outfit Mirabel Tours conducts adventure and birding trips to see the lily-strewn lakes of Khankaisky State Nature Reserve and the mink population of the Far Eastern Marine Reserve, an archipelago that has the honor of being Russia’s only marine reserve.
The rugged canyons and peaks of Sequoia and Kings Canyon National Parks, centered around the Sierra Nevada of eastern California, harbor a vast array of ecosystems. Mount Whitney’s 14,491-foot peak is the highest in the lower 48. The namesake giant trees are the star attractions, but the cave system is equally important: the park contains half of all the significant caves in California.
Ulu Segama-Malua Reserve, Malaysia
They’re home to 3,000 orangutans, but the pristine forests of Ulu Segama-Malua are under intense pressure. Ironically, much of the land is being cleared to farm palm oil, a key ingredient in biofuel.
How to Go: Visitors can explore this challenging region on an Abercrombie & Kent custom itinerary; don’t miss a suggested side trip into Sepilok Forest Reserve to see the feeding of orphaned orangutans at the Orangutan Rehabilitation Center.
At the heart of the vast Amazon basin is a UNESCO Biosphere Reserve that’s considered to contain the greatest diversity of animals on earth; one in 10 known species on earth live here. This ecological Eden, covering 1.7 billion acres, is home to 30-foot-long green anacondas, freshwater dolphins, and catfish that live on land and breathe air.
How to Go: Head deep into the Pacaya Samiria Reserve on a five-day Travcoa custom itinerary, part of it spent aboard the m/v Aqua, the first true luxury ship to cruise the northern Amazon. Activities include seeking out giant river otters and fishing for piranha.
Santa Elena and Monteverde Cloud Forest Reserves, Costa Rica
After scientist George Powell’s initial purchase of 810 acres in 1972, this protected area now covers almost 30,000 acres. Here, it’s cloud mist, rather than rain, that creates the moist climate. You’ll find more than 30 varieties of hummingbird, as well as the exotically named (and outrageously plumed) resplendent quetzal.