At the Mountains of Madness (1931) by H.P. Lovecraft : When Frankenstein's Creature went bounding off into the Arctic wastes at the end of Mary Shelley's Frankenstein in the early 1800's, ostensibly to commit suicide, he helped start a small but rewarding sub-genre of horror: the Sublime voyage into the Arctic (or Antarctic) wastes. Shelley's unnatural Creature was repeatedly associated in Shelley's novel with the great Romantic obsession, the Sublime in nature: he inexorably leads his creator on a chase after him into the Arctic, and he's repeatedly seen against the backdrop of the Swiss Alps, nimble as a goat but much, much, much larger.
One of the uses of the Sublime in literature and art of the late 18th and early 19th centuries was as a statement on the ephemerality of humanity's constructions. This use explains why there are so many paintings from that period featuring a ruined building of some sort with a mountain looming in the background. Seriously. You can look it up. And the first age of Arctic exploration was underway as the 19th century began, leading to an entire landscape of the Sublime, rather than just one looming mountain.
That a lot of these real expeditions suffered grievous losses while looking for things like the Northwest Passage just increased their literary appeal -- as did the gradual exploration of the Antarctic coast during the middle part of the century. Those first tentative forays into Antarctic exploration led to Edgar Allan Poe's Antarctic nightmare The Narrative of Arthur Gordon Pym, as well as Samuel Taylor Coleridge's "The Rime of the Ancient Mariner."
Further Antarctic exploration would be one of the exploratory high points of the early 20th century, as would the seemingly Sisyphean race to climb Mount Everest. From these two contemporary Sublime enterprises -- and literary forebears that included Coleridge, Shelley, and Poe -- H.P. Lovecraft would forge his extraordinarily influential short novel, At the Mountains of Madness. The DNA of Lovecraft's creation would have many ancestors -- including the indifferent science fictional universe of H.G. Wells, in which humanity just isn't all that important -- but the final product would be something new and enduring.
Much of the pleasure of the novel lies in its gradual, vise-tightening approach to revelations both visceral and existential, accompanied by, and accomplished by, the accumulation of telling detail. Its bare bones would be in use soon after its mid-1930's magazine publication, in John W. Campbell's "Who Goes There?", which would be adapted three times and counting into movies, always as The Thing. There, as in At the Mountains of Madness, an Antarctic expedition encounters something alien. Bad things happen. Very bad things.
Lovecraft deploys his signature documentary meticulousness here, as his narrator grinds through detailed descriptions of the foreboding landscape in order to build to the introduction of the fantastic. The details seem plausible even now, even the biological ones -- more plausible than, say, the similarly themed Prometheus. This is quite a feat for Lovecraft, as neither DNA nor the true timescale of the universe were known when he was writing. His narrative even goes all-in on plate tectonics, which in the 1930's was a theory held in contempt by mainstream geologists. So, like, score one for HPL's prescience.
At the Mountains of Madness really is a joy to read, perhaps Lovecraft's most sustained and modulated piece of horror writing. The final revelation may fall a bit flat, but I'm not sure it can do anything else, given the revelations already in play. Lovecraft's intrepid explorers find themselves not only dwarfed by a Sublime landscape -- they find themselves poised over a cyclopean Time Abyss which becomes more unsettling and unnerving the farther they physically travel into the unknown. In the end, only one revelation is comforting. And it's not that comforting.
Given how much of the novel is given over to description and exposition and people walking through tunnels looking at stuff, I'm not sure how Guillermo del Toro intended to adapt it as a movie. Like Moby Dick, which I'm pretty sure also brought some influence to bear on Lovecraft, this is an adventure novel of ideas and philosophical speculation. But what awaits at the literal and figurative bottom of the world is ultimately one step beyond rational explanation. Highly recommended.