El Dorado (Spanish for 'the gilded one') is a legend that began with the story of a South American tribal chief who covered himself with gold dust and would dive into a lake of pure mountain water.
As the story was told and re-told, El Dorado came to be viewed as a city containing immense wealth, a legend that inspired many explorers from the 1500s on.
Just on a current note, I have spent a lot of time working up the Orinoco in Venezuela. Even to this day villagers will encourage the unwary or naive traveller by pointing upstream and saying "this way to the City of Gold". Once the traveller is alone in a lonely spot the villagers have his gold!