The Old Library is a Side Quest in Assassin’s Creed Origins. This walkthrough shows how to complete the quest.
Recommended Level: 18
Region: Ka-Khem Nome
Requirement: Workers’ Lament
Reward: 1500 XP
Objectives:
- Explore the East bank of the Nile
- Reach the bandit camp
- Find and steal the Sword of Ptah
During the quest, Workers’ Lament, you should have picked up a scroll from the Temple of Horus near Baba that will give you the side quest The Old Library. Refer to that quest for details on how to get there.
The scroll that Bayek discovers in the Temple of Horus describes a mighty weapon called the Sword of Ptah, and the site of a battle where it was used. Travel to that location to discover its fate.
Once there, approach the temple to trigger a cutscene.
Turns out that the temple has been looted, and the bandits who have the sword camp to the north. Search the area with Senu to find the bandits you’re looking for at Dasos Hideout. 
Once you get there however, you discover your mistake. Turns out the bandits don’t keep the sword in the camp, but instead in a nearby cavern full of hyena. Jump in and grab the sword, then run for your life!
Or just kill the hyena with your bow? That’s what I did
or do what i did and just massacer them all with the sword u got.
It is in fact possible to unlock this one without Workers Lament. The scrolls are in there anyway and can be accessed through the temple of Horus. In such case, connection with the well seems to be blocked, however.
There’s an opening that has a tree above it where the hyenas lie. It’s perfect to snipe them or drop some fore bombs on top. I did the latter.
I wanted it for my collection of full legendary gear I couldn’t find a langdery sword so this was helpful