Tomb of Battos (Location)
Activate the Founding Father side quest right outside the Tomb before exploring it, otherwise you'll just be doubling your work.
There's no ground floor entrance, instead climb any outer pillar and dive right in.
The papyrus riddle is on a desk in the northwest, toward the top of the stairs. Snagging it yields the Underground Currents Papyrus Riddle, and completes the location.