Tanzania's Serengeti National Park is the oldest and most well-known national park in Africa, and travelers won't want to miss the sight of the world's largest and longest over-land migration. Each year, hundreds of thousands of zebras, wildebeasts, gazelle and other animals travel more than 500 miles through Mara-Serengeti ecosystem. Even in the “off-season,” plenty of animals can be seen across the Serengeti plains, making this an ideal nature travel destination any time of year.