In Assassin's Creed Valhalla Siege of Paris, you will come across Offering Altars. On this page, you will learn where to find these altars. This will make it easier for you to max out the Melunois region.
You will find the offering altar in the eastern part of the region, between the rivers.
You need 3 European Pond Turtles to complete this side activity.
You will find the turtles in a small pond a hundred metres north of the altar. You can easily shoot them with a bow. Just remember not to enter the water too quickly or they will pick up speed and quickly run away.