Greystoke Mahale sits on a pristine, white sandy beach overlooking the turquoise water of Lake Tanganyika, with the forested slopes of the 8,000-foot Mahale Mountains rising behind. It's no exaggeration to say there's nowhere in the world like Greystoke Mahale.

Home to the longest barrier reef in the Western Hemisphere, Belize has long been popular with scuba divers who head to the island of Ambergris Cay to float among the manta rays, turtles, dolphins and sharks. As of late, however, travelers are heading inland to hike in a rainforest full of parrots...