10 great places on Earth you don't want to miss

— -- In anticipation of Earth Day on Wednesday, now is a good time to focus on some of our planet's unique — and endangered — travel destinations. Holly Hughes, author of the new Frommer's 500 Places to See Before They Disappear, shares some with Tim Smight for USA TODAY.

Mount KilimanjaroTanzania 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," Hughes says. "A combination of reduced snowfall, evaporation and internal heat from the dormant volcano are to blame." Guided excursions are available for those who would like to climb this icon before the snows vanish. tanzaniaparks.com/kili.html

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. "More than 1 million tourists visit this ancient city every year, putting tremendous stress on the sandstone temples, stairs and walkways," Hughes says. "It's one of the world's most endangered classical sites, and the Cambodian government may have to impose stricter quotas or even close certain buildings in the very near future." tourismcambodia.com/attractions/angkor

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. "The effects of acid rain, encroaching development and harmful invasive species are taking a toll here," Hughes says. "But 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. You'll see white-tailed deer, beaver, and, if you're lucky, you may spy a red fox or even a moose." 518-846-8016; adirondacks.org

The EvergladesSouth 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. "An estimated 50% of this unique ecosystem has already been lost to development," Hughes says. "Dwindling water levels and pollution are compromising what remains." nps.gov/ever