Story here. There's always terror at the edge of Wells's vision, linked to his awareness of how much humanity has to lose. A line that delivers a characteristic Wellsian frisson --
“The seeing had become purblind so gradually that they scarcely noticed their loss.”
Wells wrote elsewhere that “history is a race between education and catastrophe.” In his fiction, catastrophe tends to be in the lead.
Maybe the story's opening seems slow today? A hundred years ago, the idea of an undiscovered South American valley was still plausible enough to merit extensive scene-setting. The hero's final dilemma encapsulates the timeless frustration of the visionary, confronted by a spouse-to-be who wants him to settle down and conform.
Back in the early 1990s, I argued with a friend about how exactly this story ended – neither of us had read the story since childhood, and she and I remembered the ending utterly differently. Our disagreement was understandable, since the ending is subtly ambiguous. According to Patrick Parrinder – to quote the abstract of a paper in “Science Fiction Studies” --
“Study of Wells's manuscripts shows that the author only arrived at this ending after considerable hesitation and indecision. In three surviving earlier versions, Nunez is apparently unable to break his emotional ties with the people of the valley. Through successive revisions, Wells was able to achieve a much richer and more complex ending for his story.”