The Stone Circles are 12 interactive locations found throughout Egypt. They are all part of a side quest called Bayek's Promise. Most regions have at least 1 Stone Circle in them. A few have a pair of them. Each will have Bayek align a glyph in the sky with a constellation corresponding to one of the gods or other divine figures.

This can lead to the Sphinx when all 12 have been found and activated. To complete the challenge inside the Sphnix, be sure that you have at least 50 Silica.