I made a search with Astra for other pyramids and found one in the Ural Mountains. Went to the location and looked inside using x-ray vision, this place was different, the cultists in here are not hostile. I didn't bother going inside because their specific grimoires were available in the left storage room.

Searched online with Bing and found this:
https://www.monkeyandelf.com/a-huge-pyramid-was-discovered-in-the-ural-mountains/

So it's definitely there.