Archives are a new addition to Assassin's Creed Odyssey: Judgment of Atlantis. They are locations where you can find many items giving you knowledge of Isu. Thanks to them, you will quickly develop your character.
The Tinia Archive is located in the southern part of Oikos of Atlantis.
The entrance to the archive is at the bottom of the building. You can notice it easily because the door glows golden.
This location is full of enemies. You can try to eliminate them stealthily or just rush into battle. Remember that there won't be any reinforcements - you can try to face the enemies in a regular fight.
A chest is located between the walls on the left side of the building. Open it to get an Adamant ingot.
The most important chest (containing knowledge) in this location is in the small room. You will notice it immediately thanks to the monument located directly in front of the entrance - see the picture above.