Jules Verne, "Journey to the Centre of the Earth" (1837)

A classic work, I read this as a bit of a "before bed" intellectual palate-cleanser. It's an intriguing story, but doesn't necessarily wear well with age. There are some rather implausible propositions, such as the suggestion that the narrator, his uncle, and their Icelandic guide walk (through subterranean caverns) from Iceland to southern Italy. More importantly, in the last 170 years or so, we've made tremendous progress in terms of learning about the earth, and on this knowledge it's difficult to suspend disbelief enough to fully engage with Verne's tale. Nonetheless, it is stories such as these that motivated generations of science fiction writers, and I can see how such tales could also lie deep in the roots of allohistory.