Har'akir was originally introduced to check one of the classic boxes of horror - The Mummy. Made the year after Frakenstein and Dracula, the Mummy starred Boris Karloff (probably more famous for playing Frakenstein's monster, but this role's a pretty big one too) The Mummy is about an ancient Egyptian priest who had been cursed and buried alive for sacrilege, and is uncovered by a group of western archaeologists who accidentally resurrect him. For those of my generation, the 1999 remake starring Rachel Weisz and Brendan Fraser is probably more accessible, but the general vibe is the same - adventure movie with horror elements.
Har'akir I think was very much conceived originally in that adventurous "exotic locale" mode, and I think there's been more effort in Van Richten's to allow adventurers in Har'akir to be less colonialist outsiders coming into another culture and more people who have grown up a part of Har'akir's culture.
The influence of Ancient Egypt on our cultural imagination is huge, and is particularly tied to the adventure genre from which D&D borrows a lot, as fraught with imperialism and colonialism as that genre is. But the model for just about any "ancient tomb" with "forgotten gods" in basically any fantasy story has got to be Ancient Egypt. The idea of "cyclopean architecture" surely looks back to the Pyramids and the various ancient cities swallowed by the Sahara.
The story of Har'akir, or more specifically its Dark Lord Ankhtepot, borrows heavily from The Mummy's Imhotep, but changes a few things. Ankhtepot, like Imhotep, was not a pharaoh but a priest. But Ankhtepot conspired to assassinate a young pharaoh and he and his priests were seized by the people. Ankhtepot was cursed to remain conscious as his body was mummified and then left in a sarcophagus alone with his thoughts until all memory of his name was forgotten, and only then did the Dark Powers reach out to him and grant him a domain of dread to call his own - Har'akir.
Ankhtepot is cursed with what seems like a blessing - he is completely immortal, and rules over Har'akir without any fear of losing his power. But with a part of his soul missing as part of his curse, this existence is torture.
Now, Egyptian tombs are the primary basis for your classic "deadly dungeon." Pyramids and other tombs were sometimes trapped to discourage (or stop) tomb robbers, and some had false tombs to prevent tomb robbers from finding the actual remains of the person buried there. I don't know that there's ever been anything quite so sophisticated as the blow-darts, closing stone doors, spikes, and giant rolling boulder from the cold open to Raiders of the Lost Ark, but you get the idea.
In fact, I've always pictured the Tomb of Horrors, the infamous early dungeon module that Gary Gygax created solely because his players thought the game was too easy (and was updated for 5E in Tales from the Yawning Portal,) as having a vaguely Egyptian vibe, found somewhere in a desert.
In Har'akir, one of the interesting concepts is that the vast desert land covers up countless subterranean dungeons - and that they all connect into one massive network. You could cross through the mists and find yourself in some dusty old tomb, and you might spend your entire time in Har'akir just moving through this single massive complex of dungeons.
In fact, I could imagine an entire campaign in which the entire goal the party has is simply to find a way to the surface.
Har'akir is not a small place, and so the amount of stuff below the sands is mind-boggling - which is why it's important to remember that the Domains of Dread operate on nightmare logic. Yes, in any real world, you'd never get enough stuff to fill a dungeon complex that large, and constructing it would take an absurd amount of time, resources, and effort. But because the Dark Powers just kind of willed this place into existence to serve as Ankhtepot's prison, you never have to justify it.