The Idea Factory - The Down Below
Deep under the ground of the Saharan desert, there is a huge complex that had landed in the area centuries ago, back when the desert was still an ocean. Over the years, the sands have buried it, and the pyramids were built on top of them, a poor man's facsimile to the truth buried beneath them.
Of all the people that go missing every year, about ten percent of them are abducted by these structures. They arrive within a space that doesn't look like it's enclosed. The sky is still bright above, with clouds moving past it. But as they move through the space, the people are quick to realize that they are trapped within there. Technology of the sections vary, with the center of the space having quite modern development.
The main character is a recent arrival to the space, but not the concept. They heard of similar structures in other regions of the world. While most of the people that go missing are never heard from again, one such structure was destroyed. Only those that managed to destroy the structure were the ones to escape, dooming the rest to die as the place fell in on itself. The main is trying to find a way out of there without having to destroy it and condemn everyone within to die.
With the center having very advanced technology, even some fossil fuels that they burn, in a space that is smaller than the world, climate change is running rampant in that section. But the other spaces (making something of a 5x5 grid) show less impact, with reduced movement of atmosphere between them.