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 max out the Glowecestrescire region.
You will find this offering altar in the southern part of the region, right next to the synchronization point.
You need 10 bullheads to complete this side activity – you can catch them in the nearby rivers.