Namibia and Botswana
"The river that never finds the sea" is one of nature's great miracles. Every year, when it seems as if the land in southern Africa cannot get any drier or more lifeless, an arid basin, the Okavango Delta floods with water from the river of the same name and one of Earth's most massive migrations begins. Hundreds of thousands of birds, fish, and wildlife descend on the delta as the life-giving waters sprout new vegetation and, consequently, one of the world's largest and most diverse ecosystems. The teeming oasis is a sight best viewed from the sky in the flood months from February to April. By land, the best time to see wildlife is from May to October, when animal life is more concentrated in the drying basin.
Fun fact: At its most flooded, the Delta covers an expanse almost equal to the size of Wales.