At The Mountains Of
Madness by H. P. Lovecraft
H. P. Lovecraft is most known for horror stories in general, and the "Cthulhu Mythos" in particular. As such, there are wide differences in how SF readers react to him or what expectations they have before reading him. I would, at least, categorize most of his work as "horror / SF" for a couple of reasons. First, the horror element in most of his stories doesn't focus on traditional themes (ghosts, the devil, vampires, axe murders, etc.) Rather, he uses bizarre beings from some other realm. Second, although there are some (actual or apparent) magical elements, there are various elements that have led some experts to interpret the Cthulhu Mythos as being based on two extraterrestrial races having fought over the Earth in prehistoric times. At The Mountains Of Madness provides much of the framework for viewing the Mythos in that way.
Within this context, At The Mountains Of Madness seems to be Lovecraft's most SF work. It is not set in the backwards country towns of New England. It has the relatively unearthly setting of an Antarctic expedition. The characters aren't country folk, average passers-by or antiquarians studying mystical texts. They are scientific explorers. And they find evidence that physical beings once lived there in a physical city. Clearly, in this story we are not just dealing with superstitious mumbo jumbo.
I have seen the word "supernatural" used in relation to this story. If one means by that "outside typical human experience" or "beyond what humans have previously seen on Earth", that could certainly be accurate. However, I can't see its use in the sense of spirits, deities, demons or things outside the laws of physics.
There is a horror element, and it has been described as inspired by or carrying on from Edgar Allen Poe's Arthur Gordon Pym. It is written within the confines of the science of the 1930s, at least aside from indications of what the beings who once lived there had done.
The story is presented as a narrative by a professor who has returned from a geological research expedition to Antarctica. After hearing there are plans to send a further expedition, he feels compelled to publicly state his experiences in hopes of discouraging any more trips there. During the expedition he was on, his team made incredible discoveries.
First, some frozen creatures, not part of the known evolutionary history of Earth life, are found by one group on the expedition. The specimens were deep in a cave among a geological layer too old for complex Earth life. Then, communications is lost with that group. They are later found dead, with tracks leading towards a previously unknown mountain range. On investigating, they find the ruins of a prehistoric city on the other side of the mountains.
They land a small plane nearby. The city has been mostly covered by glaciers, with only the tops of some buildings protruding out to provide a means of entry. Their explorations in the buried city show them the immense age of the city, the non-human nature of its previous inhabitants and clues to their nature and history.
There are also hints of danger and strange things. Among other things is the frightening behavior of penguins below the surface. Whether they are in the buried city or caves, it all has the confined mood of being underground. And there is the general isolation of being in an obscure corner of Antarctica - which is not a place especially hospitable to humans.
The explorers press on, driven as scientists are when given something which promises to fundamentally change human knowledge. Yet there is foreboding and disturbing sights. From various artifacts, they start piecing together the story of the aliens and indications of menace. Finally, they are forced to flee.
Perhaps this general theme could be resurrected today. Imagine a story in which global warming has melted enough of the Antarctic ice cap to uncover prehistoric ruins...
Lovecraft's works are certainly a matter of taste. This is probably not for those who generally dislike horror, for those looking for hi-tech, for those looking for an examination of lofty ideas, or for those who need the kind of writing style English professors ooh and aah over. Others, especially those open to SF of the 1930 and 1940s, may enjoy it. At least for those who can appreciate the horror aspect, this may actually be more enduring than most SF of that period.