Yaru: At the top of the shadow of the only bird's-eye view point.
Aton: There is a Sphinx next to the Reflection Room point in the upper right corner of the map, and then there is a room behind it. There is a gap in the room.
Underworld: There is a gap under the large water tank in the lower left corner of the map.
Hebside: Do you still remember the fight with the Emperor? There are footprints under the cliff on the left side in front of the Emperor's chair. Just follow the footprints (there is a snake inside).