2. Zambezi (Africa)
Scenic beauty: 5 | Nature and wildlife: 4 | Culture: 4 | Adventure: 5 | Activity options: 4
Boasting superb wildlife watching, some of the best white-water rafting on the planet and the thundering beauty of Victoria Falls, the Zambezi is a showstopper.
In the Middle Zambezi, which borders Zambia and Zimbabwe, you can bungee jump off Africa's largest waterfall, or tackle the grade IV rapids just below.
Most wildlife -- from hippo pods to big cats and sly Nile crocodiles -- is spotted on jeep safaris and kayaking trips around the Lower Zambezi, where the swampy delta funnels down through Mozambique into the Indian Ocean.
1. Amazon River (South America)
Scenic beauty: 5 | Nature and wildlife: 5 | Culture: 4 | Adventure: 5 | Activity options: 5
Topping our list by an aquatic mile, the mighty Amazon snakes through the jungles of nine South American nations, providing a sanctuary for more than 400 indigenous Indian tribes and one in 10 of the known species on earth.
For travelers, the possibilities are huge -- from wildlife spotting safaris to kayaking trips and gnarly jungle treks.
Backpacker-friendly Bolivia is a popular place to explore the pampas by lancha (long-tail boat), stopping off along Amazon tributaries to swim with pink dolphins, fish for piranha and track elusive anaconda.