Based on a book I read a couple years ago, with the same title. This is a fictionalized version of Percy Fawcett's (Charlie Hunnam) life, particularly his trips to the Amazon. It was interesting to see what they did with the story taking it from a non-fiction book to the screen.
You'll find a couple negative reviews of Hunnam's previous acting if you look around in my movie reviews - but I thought he was really good here. Everyone else was good too, particularly Robert Pattinson in a somewhat subdued role as his second in command. The movie shows how horrible exploring the Amazon could be, and how long (years, and several times) he was away from his family.
But ... I should stay away from stuff I know ends badly, because that's just no fun during a pandemic. No one knows what the hell happened to Fawcett and his son: they went into the jungle in 1925, they didn't come out: director James Gray has given them a much more spiritual end than I think is likely. But the movie is mostly accurate to my memory of the book. They leave out a huge amount of detail - including some of the less appealing parts of Fawcett's personality - as is necessary to fit into a two hour twenty minute movie.