Understanding 'Unsettling' in Context

In the text, the author describes the protagonist's journey through a tumultuous landscape. At one point, they encounter a deep ravine that seems perilous. The author writes, "As they peered into the abyss, an unsettling feeling washed over them, a foreboding sense that the chasm held more than just darkness; it concealed the weight of unspoken fears and lost hopes." In this context, what does the word 'unsettling' convey about the protagonist's emotions?