The Mountains of Madness

'The last lap of the voyage was vivid and fancy-stirring, great barren peaks of mystery looming up constantly against the west as the low northern sun of noon or the still lower horizon-grazing southern sun of midnight poured its hazy reddish rays over the white snow, bluish ice and water lanes, and black bits of exposed granite slope. Through the desolate summits swept raging intermittent gusts of the terrible antarctic wind; whose cadences sometimes held vague suggestions of a wild and half-sentient musical piping, with notes extending over a wide range, and which for some subconscious mnemonic reason seemed to me disquieting and even dimly terrible. Something about the scene reminded me of the strange and disturbing Asian paintings of Nicholas Roerich, and of the still stranger and more disturbing descriptions of the evilly fabled plateau of Leng which occur in the dreaded Necronomicon of the mad Arab Abdul Alhazred. I was rather sorry, later on, that I had ever looked into that monstrous book at the college library.'

- H. P. Lovecraft - At the Mountains of Madness, 1936

Nicholas Roerich, Milarepa, the One Who Harkened, 1925 

Nicholas Roerich's 'strange and disturbing' Asian paintings are mentioned several times in Lovecraft's novel.  A character notices 'odd formations on slopes of highest mountains. Great low square blocks with exactly vertical sides, and rectangular lines of low vertical ramparts, like the old Asian castles clinging to steep mountains in Roerich’s paintings.'  Later the narrator says 'There was indeed something hauntingly Roerich-like about this whole unearthly continent of mountainous mystery.' Finally, at the end of the story, after the horror of the mountains of madness is revealed:

'From these foothills the black, ruin-crusted slopes reared up starkly and hideously against the east, again reminding us of those strange Asian paintings of Nicholas Roerich; and when we thought of the damnable honeycombs inside them, and of the frightful amorphous entities that might have pushed their foetidly squirming way even to the topmost hollow pinnacles, we could not face without panic the prospect of again sailing by those suggestive skyward cave-mouths where the wind made sounds like an evil musical piping over a wide range.'

Nicholas Roerich, Himalayas, 1933

Various Lovecraft bloggers have mentioned Roerich and posted images of his art.  One quotes a letter Lovecraft wrote in 1930: "surely Roerich is one of those rare fantastic souls who have glimpsed the grotesque, terrible secrets outside space & beyond time, & who have retained some ability to hint at the marvels they have seen."  Lovecraft was able to see these paintings at the Nicholas Roerich museum, established in New York in 1929.  In that same year Roerich was nominated for the Nobel Peace Prize - the Roerich Pact protecting cultural property in war is named after him.  It would be hard to briefly summarise his extraordinary life up until that point - it included a long trip through Russia painting its architecture, set designs for Diaghilev (including The Rite of Spring), the creation of a mystical sect in London and then the epic Journey Through Asia that inspired the paintings Lovecraft admired.  You can read the story of this expedition, in which Roerich hoped to find the hidden land of Shambhala, in an Atlas Obscura article 'Why the Soviets Sponsored a Doomed Expedition to a Hollow Earth Kingdom.'  Roerich's own experiences sound very much like those of a Lovecraftian explorer:

It is said that the closer one approaches to the hidden, hollow-earth city, the more vague their writings become, because Shambhala cannot be described in mere words. In his esoteric book Shambhala the Resplendent, which he was writing along with his more scientific and much drier travel diary, Nicholas began charting another, parallel journey written in stories and riddles. As the expedition went deeper, he increasingly recorded strange manifestations, fires, lights and visions over their camp —though those were mostly left out of his scientifically-minded travel diary. His paintings also became more esoteric, increasingly depicting the messianic King of Shambhala. ... Communication was lost, and the Roerichs were considered dead. [Eventually, after a year, they reemerged in India, having been detained in Tibet where five expedition members died.]   The closest they had gotten to Shambhala, according to Nicholas’ travel diaries, was in the Altai mountains, in the valley of Uimon, when an “Old Believer” proudly showed them the entrance to the subterranean kingdom, now barred with stones.