Fabled city (2,6)
'fabled city' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for el dorado that I've seen before include "Golden land imagined by the Spanish explorers of America" , "Imaginary land of riches" , "Fabled place of wealth" , "'Imaginary place of great wealth and opportunity (2,6)'" , "Place of great wealth, from fictitious city on the Amazon" .)
(Other definitions for eldorado that I've seen before include "The golden land?" , "city of riches" , "a place of great wealth" , "source of wealth" , "rich land, so many thought" .)