Where It All Goes Down
The Contemporary Real World (Assuming Ancient Egyptian Myths and Magic Are Real)
Who said the Egyptian gods were confined to ancient Egypt? In The Red Pyramid, the gods and their way of life have survived into the modern day—but most modern mortals are too ignorant about the supernatural to know it.
Date, Date, Who's Got a Date?
The precise year of the novel isn't so important, as long as you can get a general feel for what's going on. We imagine the novel's set in the early twenty-first century, for a few reasons. First, when Inspector Williams questions Sadie after her father blew up the British Museum, the inspector accuses Julius Kane of either being a terrorist or being in league with terrorists: "There are extremist groups in Egypt that object to Egyptian artifacts being kept in other countries' museums. These people might have approached your father" (3.56). Terrorism, of course, became a greater concern in the late twentieth and early twenty-first centuries.
On top of that, when Bast and the kids are trying to reach Phoenix as part of their save-the-world Great American Road trip, they "borrow" an RV. It's described as "a FEMA leftover from Hurricane Katrina" (29.3). So we know that the novel is set in 2005 or later, since Katrina occurred in August 2005.
Geography:
Magical and Mundane
The geographical locations are more fixed than the exact date, since Sadie and Carter travel a lot and describe each place they visit, from London to the Cairo Airport. They see large swaths of the United States, since they need to travel to Phoenix to stop Set's red pyramid time bomb there. They run into a bunch of mortal landmarks—Graceland, the Rio Grande, and New Orleans—but they also see a ton of magical sites, too.
Of the many magician headquarters, or Nomes (there are three hundred and sixty in all), we only get close-up glimpses of two: the First Nome (in Egypt) and the Twenty-first Nome (in Brooklyn, New York). The First Nome of course is quite large and filled with magicians, though we get the impression that there used to be more.
The First Nome runs under much of modern Cairo, and it's not unique in that regard: a lot of magical spaces overlap with the mundane world (sort of like they do in Harry Potter). As Zia explains it, the magicians closed off the tunnels under the Sphinx and other monuments because archaeologists were getting too curious; they were on the verge of learning how much the magicians were hiding from them.
Carter at one point asks Zia about the Three-hundred-and-sixtieth Nome. Maybe he means it as a joke, but Zia answers seriously, telling him that it's Antarctica: "A punishment assignment. Nothing there but a couple of cold magicians and some magic penguins" (13.84).
Magic penguins and magicians suspected of being terrorists: that about sums it up. It's like our world—but weirder and full of more supernatural stuff.