Mount Kilimanjaro: Tanzania
Rising majestically to a height of 19,330 feet, Mount Kilimanjaro is Africa's tallest peak. But its famed snow cap is shrinking. "More than a third of it has melted since 1990. A combination of reduced snowfall, evaporation and internal heat from the dormant volcano are to blame.
Angkor Wat: Siem Reap, Cambodia
The capital of the Khmer kingdom from 802 to 1295, Angkor Wat is Cambodia's chief tourist attraction — temples and shrines that cover 38 square miles.
Adirondack State Park: Upper New York State
Established in 1892, this 6 million-acre park encompasses more than 3,000 lakes and ponds connected by 1,500 miles of waterways. Much of the park's heart has been kept inaccessible to vehicles, preserving a slice of wilderness. The best way to appreciate it is to canoe through its quiet rivers and forested lakes.
The Everglades: South Florida
A waterworld of mangrove swamps and grassy wetlands, the Florida Everglades is home to rare plant and animal species including manatees, hawksbill turtles and American crocodiles.
Valley of the Kings: Luxor, Egypt
More than 60 subterranean crypts of ancient Egyptian pharaohs have been unearthed at this legendary archaeological site. The tombs are still open on a rotating basis. If you're lucky, you may be able to see the burial chambers of King Ramses VI or King Tutankhamen.
Michoacán Monarch Biosphere Reserve: Mexico
Each year, tens of thousands of monarch butterflies complete a 2,000-mile migration between Canada and their winter nesting grounds in the mountains of Mexico. The reserve is reachable by day trip from the Colonial-era city of Morelia — allow 10 to 12 hours for a guided excursion.
The Dead Sea: Israel
Surrounded by desert ridges interspersed with lush oases, the Dead Sea presents a visually stunning tableau. But with the upstream Jordan River increasingly diverted for irrigation, the water level of this huge inland lake has been dropping at an alarming rate. Scientists estimate that within three decades, the Dead Sea could be completely dry.
The Nazca Lines: Peru
One of the most intriguing and mystifying ancient sites — believed to have been created by the Nazca, a culture that flourished around 300 B.C. — is on a high, arid plateau about 300 miles south of Lima. A hummingbird, spider, and a monkey are among the more than 30 elaborate figures etched into the plain. Hundreds of feet in diameter, the drawings can only be seen in their true dimensions from the sky.
Piazza San Marco: Venice
"Sitting in the heart of Venice, Piazza San Marco is arguably the loveliest public space in the world — a huge open square fronted by the magnificent St. Mark's Basilica. Since the 1980s, the piazza has been underwater more than 40 times per year. The time to see it may be growing short. Scientists estimate that this iconic city is sinking at the rate of 2½ inches a year, and rising sea levels in the Adriatic make flooding a constant concern.
Tasmania Overland Track: Tasmania
Off the coast of southern Australia, Tasmania encompasses one of the world's more unusual ecosystems. Running through the island's center like a spine is the Overland Track, a 40-mile trail that traverses high alpine plateaus, marshy plains, eucalyptus groves and one of the planet's last temperate rain forests. Many unique species can be viewed along this famous trail, including the island's 'mascot' — the Tasmanian devil. Read More About Tasmania