In Assassin's Creed Valhalla, you can find Offering Altars. On this page of the guide you will learn where to find the altars. This will make it easier for you to complete Ledecestrescire region in 100%.
The offering altar can be found in the northern part of the map, near the border with another region.
This particular Offering Altar requires you to sacrifice a few/more than a dozen of rabbits. There are many of them running in the area, so you will have where to hunt. You must collect 5 hare's foot. Remember that hare's foot might not fall from every single defeated rabbit. You must kill enough of them to obtain the number of hare's foot required for the sacrifice.