This riverside orangutan rehabilitation camp is usually reachable only by boat. For times when the Sekonyer Kanan River runs dry, volunteers are building a 2.5-mile boardwalk to the camp. Workers are often approached by two curious orangutans, a welcome interruption following a busy day in the humid rain forest. —Kellie Schmitt
The Orangutan Foundation: About $1,400 for six weeks, including building materials, lodging, and food. 44/(0) 207-724-2912, orangutan.org.uk.