Heart of Darkness is a great text, short but dense. Read stuff about it as well as just read it. Physical journey promotes real change in character, lots of techniques towrite about.
I guess the easiest way round that is to say it's a poem, it's fiction, so it must be imaginative to some degree, right? The usual poertry techniques, but especially symbolism. And as to physical journey, so you take the line that sh euses physicla symbols ot represent other things, you can say...