About 2 years ago I ran a campaign in a small settlement on a caravan route in the deserts of eastern Shem...
The settlement was built around a lone purple tower. The Tower was recently re-inhabitated by a Stygian Wizard, players ran afoul of the wizard and ended up in the catacombs below the tower which also stretched out throughout the small city. The walls were of a strange green stone of cyclopean size.
They eventually found a room, that glowed softly in which was a lone sarcophagus showing the image of a tall man like figure with reptillian features. On a pedestal nearby was an ancient tome, which thankfully one of the players opened. Though the writing was incomprehensible, words were repeated such as Cthulu and Yog Sagoth and R'lyeh. He saw visions of two of the tall snake men with glowing eyes sent by other members of the Giant Kings constructing the tower through long forgotten magic to studt the stars for signs of the coming. Player made a will save so his soul was not drawn into the tome. The Climax was a fight with a "many tentacled monster which tore the players up pretty good - two Barb's went beserk and ran after it when it mysteriously retreated. My character tripped them up, and because they ran into the pitch dark, knocked themselves out on the walls. Just as the players were leaving the catacombs, the Stygian Wizard showed up in all his power, he was reaking havoc when tentacles were seen over his shoulder and then encompassing his whole body, pulling the wizard screaming deeper into the darkness. I had actually planned the end this way so it was not a "The players are all going to die, I better change things...
I tried using recurring Howard and Lovecraft themes as well as some of Dale Rippke's treatises on Howard. Howard had the Giant Kings as an Elder Race and there description according to Rippke matched the Biblical "Watchers" from the book of Enoch I believe. Howard also used jade colored stone frequently in ruins and catacombs that lead to each dwelling in the settlement. I think both Howard and lovecraft used this kind of stone and used the term Cyclopean.
Now I did not remember R'lyeh was an Island or that Cthulu was there, but geography changes and this could once have been by the sea, and also the ancients tried to glean knowledge from the stars, so perhaps I did not corrupt it too bad...it was a fun adventure.