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 Consus Archive is located in the Northern part Of the Atlantis / Atlantic OIKOS.
The entrance to the archive is at the bottom of the building. You can notice it easily because the door glows golden.
Enter the location quietly and eliminate the enemies standing in your way. Keep moving down until you find a hidden chest.
The chest is at the bottom of the location. It is protected by a man - eliminate him first so he won't cause you problems.
On the right, next to the chest, you will find another, that contains a weapon and money.
A chest is located between the shelves. Go to it and collect an Adamant ingot.
Before you leave, check the room with corpses. Among the corpses, you will find a weapon blueprint.