In Assassin's Creed Valhalla Wrath of the Druids, 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 Ulster region.
The Morrigan's Altar
You will find the Offering Altar in the eastern part of the region, near the synchronization point.
You need 25 Luxuries to complete this side activity. You will get them by exploring the world and examining the contents of chests.