Sumatra is the world's fifth-largest island. Its center is mainly flat, with many fertile rivers running throughout and emptying into the sea. The island is home to many species, including the Sumatran orangutan and the Sumatran tiger. Visitors can see them in their habitats in the island's national parks. But these animals are endangered. Experts estimate that there are no more than 500 Sumatran tigers left in the wild. (TIM LAMAN—GETTY IMAGES)