In opposition to previous Perception of Hermes, this one differs greatly, as it is not hidden inside a cave. To get access to Veiled Altar of Hermes, you need to climb to the top and find the entrance in one of the buildings. This is one of the more important locations in Assassin's Creed: Odyssey Fate of Atlantis, as you'll visit it when completing story missions.
When you reach a wooden locked door, climb to the top of the building.
Once you get to the top of the building, continue climbing.
When you reach the top of the mountain, enter the building shown in the screenshot above. It can be found on the left side of the mountain.
There is a hole inside the building. Jump inside to get to the bottom of the mountain.
At the bottom, there is a small cave. There is a table inside. You can see it well, as it is brightly lit.