Many wonderful, interactive maps of Africa, the Congo, the Congo River, American locales and more can be found on Google Maps. I encourage teachers to both explore this themselves, and trust students – who are sometimes far more technologically inclined – to give a hand in finding the appropriate maps for the places we explore in this unit.
For an available text of Heart of Darkness, Project Gutenberg is a great resource. This can be found by copy and pasting the following url: https://www.gutenberg.org/files/219/219-h/219-h.htm