At the Mountains of Madness (1936)
H. P. Lovecraft (writer).
With the mountains—huge, stable and eminently observable—Lovecraft finally breaks out of the weird tale mold and into science fiction proper. It’s a techno-thriller of Antarctic exploration, with predictable history-altering consequences considerably larger than the general fever antidote in “The Last Test” (1928), and more believable detail than “The Mound” (1930).
Appropriately, there is a practicality, intelligence and nobility to the Elder Things that puts them well above mere monsters. Not evil, they are instead “fearfully great” in the manner that ancient Greek tragedians called deinos. I would have liked for their society to be fleshed out more. The whole story is quite schematic, with the undescribed final horror and turn against scientific curiosity merely tacked on.