"AFTER twenty-two years of nightmare and terror, saved only by a desperate conviction of the mythical source of certain impressions, I am unwilling to vouch for the truth of that which I think I found in Western Australia on the night of 17-18 July 1935. There is reason to hope that my experience was wholly or partly an hallucination—for which, indeed, abundant causes existed. And yet, its realism was so hideous that I sometimes find hope impossible.
If the thing did happen, then man must be prepared to accept notions of the cosmos, and of his own place in the seething vortex of time, whose merest mention is paralysing. He must, too, be placed on guard against a specific, lurking peril which, though it will never engulf the whole race, may impose monstrous and unguessable horrors upon certain venturesome members of it."
The Shadow Out of Time By H.P. Lovecraft 1936
H.P. Lovecraft's 1936 novella The Shadow Out Of Time has been a major inspiration for me for many years. But the one thing that seems to get forgotten is the fact that the real treasure and threat of the novella isn't the time conquering Great Race of Yith.
Reading through the Wiki entry I came across this bit; "The Shadow Out of Time indirectly tells of the Great Race of Yith, an extraterrestrial species with the ability to travel through space and time. The Yithians accomplish this by switching bodies with hosts from the intended time and place. The story implies that the effect, when seen from the outside, is similar to spiritual possession. The Yithians' original purpose was to study the history of various times and places, and they have amassed a "library city" that is filled with the past and future history of multiple races, including humans. Ultimately the Yithians use their ability to escape the destruction of their planet in another galaxy by switching bodies with a race of cone-shaped plant beings who lived 250 million years ago on Earth. The cone-shaped entities (subsequently also known as the Great Race of Yith) lived in their vast library city in what would later become Australia's Great Sandy Desert ( )"
And now the works of the Great Race of Yith have been slowly being uncovered on Earth & elsewhere. And could this be the next cause for the next extinction level event. Unless the adventurers can find their way around this. Now over the years the works of the Great Race of Yith have appeared in my games as treasures, lost technologies, artifacts, etc. But the real horror is going to be the flying polyps that could cause massive problems or die off's in old school & OSR games.
In various games of Lamentations of the Flame Princess's Carcosa, Labyrinth Lord, Stars Without Number, ACK's, and other OSR games over the years that I've run each & every time the spectre of the flying polyps have been there. These are the horrors that really guard the treasure, technology, and other relics of the Great Race of Yith.
And this gets into the real issue of using the Great Race of Yith, they are one of the most alien of Lovcraft's races. Sure they almost seem to be on level of humanity's consciousness. But in reality we are nothing more then a bit of experimentation and a target to be left for the polyps to devert their attention away from the Yithians. And this could also be exactly the reason why they'd leave behind ruins & dungeons across the multiverse.