A Pharaoh's Ka (Main Quest)
A subquest splinter of King of Kings. In this one, you need to find two crystal eyes. Search for the first in the Scorpion Lair east of the Heb Sed fast travel point.
Kill any scorpions above ground, then descend into the cavern.
Use your Animus pulse to reveal the treasure location.
Loot the altar there for the left eye of Ramsses.
There's also a scroll here with a Blade Runner reference.
The other eye is in the Maryannu camp. It's not locked up, but it being carried by a patrolling hostile.
This hostile happens to be a mummy with a penchant for resting by giant oil reserves. If you catch him in such a spot, this is a good time to go for the Pyromaniac achievement.
Loot the corpse afterward for Ramsses' Right Eye. Getting both completes the mission.