Bakchias (Location)
A small rebel outpost amongst desert cliffs and ruins in Faiyum. You'll pass through during the A Rebel Alliance side quest.
The sole treasure is in a storeroom to the north.
Head there, climb over the block wall, and drop down into the chamber on the other side.
From there, look for the passage with the ladder and the snake.
The treasure is up top in a red chest- looting it completes the mission.