They trek alongside rivers, over rough terrain and deep into the rainforest in an area that is home to numerous endangered species, from orangutans to tigers, but which has suffered devastating deforestation in recent years.
The sprawling Indonesian archipelago has large swathes of tropical forest but vast tracts are being felled to make way for palm oil and pulp and paper plantations, destroying biodiverse habitats and adding to greenhouse gas emissions.
Much of the logging that takes place is illegal as it happens outside concessions granted to companies, but it is hard for authorities to keep track. Poaching of endangered species is also common, with elephants killed for their ivory and tigers for their pelts.