We could have picked the River Li in China for its celebrated hills or the Amazon for its extraordinary variety of wildlife. But we've gone against the flow and picked an obscure little waterway in Colombia as the world's most beautiful. Caños Cristales is actually a rather ordinary river for much of the year, but for a short time between the wet and dry seasons, when the water level is just right for its unique algae and moss to flourish, it erupts into a rainbow of extraordinary colours. The river is buried deep in the Sierra de la Macarena in central Colombia, and is only accessible on foot or horseback.
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