The following is currently on my whiteboard: An Underworld temple sacred space marked by a hill or stone circle would probably make more sense. And I put it there after reacquainting myself with English archaeology and folklore, something I used to be fairly familiar with.
In fact, when I originally wrote this particular manuscript, my self-compiled book of myths and legends from the British Isles was within reach. I was so focused on telling the story in my outline, though, that I failed to think about how things actually work. For whatever reason, I took my Hollywood Egypt brain and applied it to the British Isles with a complete disregard for the cultural differences. That realization is bothering me so much that I have actually stopped working on that manuscript until I decide how I’m going to handle the issue.
What’s really bad is that I’m already rewriting the manuscript because my original outline left out the bad guys for a good 90% of the story. Even better, I completely failed to place any real emphasis on the site or the relic that are at the heart of the plot. 14,000 words into the rewrite, I’m now stopped again because the site and the relic are completely implausible for their setting.
The moral of the story here is that it is good to write what you are familiar with, but you really should write down what you think you know and do some fact-checking and research both before you start and along the way to keep yourself on track.