This location is in the northern part of Porimos Ring. This is one of the most important locations in Assassin's Creed: Odyssey Fate of Atlantis - you get here during the main storyline.
To get inside this location, you need to enter the cave located near the water. You can notice it easily because the door has a golden glow.
The location is quite simple. You have to keep walking along the wall until you reach the big room.
Before you start searching, eliminate all enemies. Do it quietly to gain an advantage.
An Isu codex t is on the left side of the room. Go to him and gather information.
If you climb up the stairs, you will see an enemy guarding a tablet. Kill him quietly, then go to the tablet and confirm the location.
There is a chest between the columns in the center of the room.
Go up the stairs. There, you will find a marble chest - it contains an Adamant Ingot.