Kilimanjaro Peak, Tanzania, 1997

Hikers begin the long, grueling trek up Kilimanjaro, Africa's highest peak. Though many are excited by the challenge and adventure, their guides call out "polepole" (PO-lay-PO-lay), the Swahili word for "slowly." At elevations over 18,000 feet (5,486 meters), moving slowly is the only way to adjust to the lack of oxygen and avoid cerebral edema.

(Text adapted from and photograph shot on assignment for, but not published in, "Hiking into the African Sky," July/August 1998, National Geographic Traveler magazine)