James Gray’s new film, Lost City of Z, takes a look at legendary British explorer Percy Fawcett’s 1925 venture into the Amazon jungle in search of a fabled civilization, from which he never returned.

The project is based on David Grann’s 2009 book of the same name and stars Sienna Miller (American Sniper) and Robert Pattinson (Twilight) alongside Charlie Hunnam. Hunnam has just finished shooting Guillermo del Toro’s film Crimson Peak and is now shooting Knights of the Round Table: King Arthur for director Guy Ritchie.

Here’s what we can reveal so far: “In 1925, Fawcett ventured into the Amazon to find an ancient civilization, hoping to make one of the most important discoveries in history. For centuries Europeans believed the world’s largest jungle concealed the glittering kingdom of El Dorado. Thousands died looking for it, leaving many scientists convinced that the Amazon was truly inimical to humans. But Fawcett, whose daring expeditions inspired Conan Doyle’s The Lost World, spent years building his scientific case. Captivating the imagination of millions round the globe, Fawcett embarked with his son, determined to prove that this ancient civilization – which he dubbed Z – existed. Then his expedition vanished.”