The author did an admirable research for information about the many and perilous attempts of
Percy Harrison Fawcett to find Z or El Dorado in the Amazon jungle. He also found a lot of data about those who attempted the same journey with more grandiose means. And we discover how dangerous the jungle, however magnificent it is, may be.
As some commentators said, this is a story of the "real" Indiana Jones.
Other reviewers found it to be repetitive. Inevitably, since Fawcett returned to the rainforest many times, without finding Z. And these reviewers are disappointed that he did not find it. But the author gives us a final clue that suggests that this city existed at some point in the past and for a long period of time. But the first Europeans who went there quickly killed the Amerindians they met (diseases, slavery, destruction of their habitat, or even genocide) and destroyed their civilization (as usual). And the forest, devourer of all that is vegetable (wooden constructions) and even mineral (stone constructions and landscapes), has almost erased all trace of what once existed there.
But as the author so well said, it's not because we find nothing or almost nothing today, that there was nothing in the past.