These days, nearly all Amazon river cruises travel upstream from Iquitos to the confluence of the Ucayali and Marañon Rivers, and the Pacaya-Samiria Reserve. However, when I first took one of these cruises, in the year 2002, the Rio Amazonas took me and my group downstream to the tri-border with Colombia and Brazil. It remains a very interesting - albeit busier - river journey, which can be visited using local transport or by chartering your own vessel.