This sprawling ancient metropolis in the jungle of Ecuador has revealed a unique form of urbanism found only in the Amazon. Sofia Quaglia visits the site for the story of this mysterious civilisation. Archaeologist Alden Yépez hikes through a field of bright green grass, swinging his rusty machete left and right to carve a path in the shoulder-height tropical pasture. He's following his handheld GPS device with a certain haste: we must make it out of the grassland before sundown. At this pace,