The horror in At the Mountains of Madness is not in sadistic descriptions of slashings, torturings, mutilations and bloodletting, but rather in the slow build-up of the feeling that humanity is not alone in the universe and that the other inhabitants, if they consider us at all, don't really think much of us. The only times the history of the Elder Things mentions us it is as either an amusing animal kept for entertainment or as a foodstuff.The horror is that there are unfathomable depths of pre-history, that humankind are very much late-comers and that, if we are not careful, we might come to the notice of things that could wipe us away with little thought.Nonetheless, the Elder Things are portrayed as one of the few, if not the only, of Lovecraft's non-human races with which we can feel any sympathy. He remarks that, despite the terrible toll they take upon the expedition, they were not evil things of their kind and that they had not acted any differently than would we in the same circumstances. The fate of the Elder Things is one that evokes a feeling of pity.I've read that this story de-mythologises the Cthulhu Mythos and recasts the stories as science fiction rather than as tales of the supernatural and cosmic horror, but I don't think that is necessarily correct. Although the Elder Things are described as being composed of normal matter and having originated somewhere within our own mundane dimension, Lovecraft specifically states that the Star Spawn of Cthulhu and the Mi-Go are composed, at least partly, of some exotic material and that their origins lie outside the realm we know. Also, credit must be given to Lovecraft's characterisation, something that he is not often accorded: the story is written from the perspective of a scientist who has interpretted the history of the Elder Things through pictorial representations. Naturally the narrator's own world-view, that of scientific materialism, infuses his interpretation.One of Lovecraft's best.