check out our:
"[…] on one end a large shining map, marked with all the colours of a rainbow. There was a vast amount of red - good to see at any time, because one knows that some real work is done in there, a deuce of a lot of blue, a little green, smears of orange, and, on the East Coast, a purple patch, to show where the jolly pioneers of progress drink the jolly lager-beer. However, I wasn't going into any of these. I was going into the yellow. Dead in the centre. And the river was there—fascinating—deadly—like a snake." (1.23)
All the colors on the map means Africa isn't a blank space any more—it's been parceled up and handed out to Western countries. But even if there's no blank space left, that river is still there.
"Watching a coast as it slips by the ship is like thinking about an enigma. There it is before you - smiling, frowning, inviting, grand, mean, insipid, or savage, and always mute with an air of whispering, 'Come and find out.'" (1.30)
Pro tip: when the coast starts talking to you, it's probably time for some shore leave.
"One day he [the accountant] remarked, without lifting his head, 'In the interior you will no doubt meet Mr. Kurtz.' On my asking who Mr. Kurtz was, he said he was a first-class agent; and seeing my disappointment at this information, he added slowly, laying down his pen, 'He is a very remarkable person.' Further questions elicited from him that Mr. Kurtz was at present in charge of a trading-post, a very important one, in the true ivory-country, at 'the very bottom of there. Sends in as much ivory as all the others put together […].'" (1.46)
Marlow wasn't too interested in Kurtz at first, but he's starting to get curious. As the details pile up—he's a first-class agent, he's a remarkable person, he sends in quantities of ivory—our hero can't help wanting to, um, explore.