What does "I were about to set off for the centre of the earth" mean here

Question

This excerpt is from Heart of Darkness, by Joseph Conrad.

After this I got embraced, told to wear flannel, be sure to write often, and so on—and I left. In the street—I don’t know why—a queer feeling came to me that I was an imposter. Odd thing that I, who used to clear out for any part of the world at twenty-four hours’ notice, with less thought than most men give to the crossing of a street, had a moment—I won’t say of hesitation, but of startled pause, before this commonplace affair. The best way I can explain it to you is by saying that, for a second or two, I felt as though, instead of going to the centre of a continent, I were about to set off for the centre of the earth.

Why does the protagonist feel that "I were about to set off for the centre of the earth"?

Answer 1

Marlow says he felt as if ("as though") he was going on a journey to the centre of the earth. This can be seen as a foreshadowing of events later in the novel, when he encounters Kurtz. Kurtz had once been described as someone who would get far in the trading company for which he worked and "the International Society for the Suppression of Savage Customs had intrusted him with the making of a report" (section 2). However, Marlow found that Kurtz "preside[d] at certain midnight dances ending with unspeakable rites".

The image of the journey to the centre of the earth creates a sense of foreboding: in Dante's Divine Comedy, for example, the centre of the earth is where the devil sits, and in Conrad's novel evil is associated with darkness (see e.g. " a treacherous appeal (...) to the hidden evil, to the profound darkness of its heart" in Section 3.) Note that Marlow tells the entire story in retrospect, so he already knew what sort of "darkness" he would encounter.